Explore the showcase, find a theme that appeals to you, and explore its fine points using the live demos and previews. I have a mental list of features I consider, and ideally they will all be present. Or at least attainable with some additional CSS code. You may or may not want or need the same things, but here are some of the things I look at:
Free or premium? First, decide if you want a free theme or a premium theme. There’s no point in even looking at the tempting premium themes if you aren’t prepared to pay for one.
Complex or simple. Some themes are beautifully, elegantly simple and may be exactly what you want. Some are very dramatic, with huge images. Some are busy-looking. Chances are the busy ones, with lots of different features and information on the home page, are that way of necessity; they are magazine- or newspaper-like designs intended to display a large variety of content. Like this theme (Opti), they’ll show featured posts, perhaps with larger images or in a slider. They have several places for widgets so you can include as many as you need to showcase your content. You have to decide whether you want your readers to explore and discover your content on their own or whether you want to attract their attention with menus, featured posts, and widgets. The most important thing, however, is to pick a theme you love, a theme you feel best shows who you are, and start writing. There are 295 other themes available if you change your mind.
Headers. There’s a header style for every taste, and that may well be where you begin your selection process. Consider whether you can or want to change the default image. Some themes include an option to upload several images that will change every time a page is refreshed. Personally, I prefer a customizable header. It’s important to me to have a unique look, something that sets this blog apart from others, especially those using the same theme. More than anything else, the header establishes your brand or trademark. Actually, I’ve fallen a bit short on that score; I deal with so many different topics that I can’t decide on a single image that illustrates this blog. So I’ve opted for no image at all. (If you’ve any suggestions, I’m all ears.)
Theme options. Different themes include different options and they may well determine your decision. The special features may include changeable headers and/or backgrounds, different sidebar arrangements, front page sliders for featured posts, font options, etc. The left sidebar on this theme’s home page, for example, shows titles from categories of my choosing. Or I can completely eliminate the sidebar.
Excerpts or full posts. Notice whether the home page displays post excerpts or full posts. Excerpts are better if you deal with a lot of different subject matter and want to display more of it on your home page; readers can then click through to read posts that interest them. If you don’t deal with a variety of topics, you might prefer the simplicity of full posts on the front page.
Dateline. Where does the theme put datelines? I consider it critical that the dateline appear at the top of each post. And it must include the year, since most websites span multiple years. If I’m looking for timely information, the first thing I do is check the date. If the item is too old to be relevant, I won’t waste time reading it. Dates aren’t always important (eg, artwork, recipes), but more often than not they are. It frustrates me to have to search for a date on something and ultimately find it only in the URL, if at all.
Width of the main column. Is it wide enough for your purposes? Do you want to display big images or galleries? Narrower measures are easier to read, but if you like big images, you’ll want to avoid narrow columns. Technology keeps advancing, and most wide themes can now be dragged to whatever width you prefer for easier reading. But wide measures or wide featured images may require you to always use larger images, which might not be easy to find for every post. I adopted one theme that I really liked, Oxygen, only to drop it a day or so later when I realized I was going to need a 750px image for every post.
Widgets and sidebars. What are the options for widgets? Does the theme put them on the left, right, and/or bottom? Is that where you like to have them? Is there a search box in the header or will you need to add one in a widget?
Fonts. Do you like the theme’s default fonts? If not, it’s easy to change them using the WordPress Customizer (requires a $30 yr. Custom Design upgrade). Fonts can really affect the feel and tone of a theme, so don’t overlook them. Light and airy. Old-fashioned. Rigid and serious. Casual or hi tech. And remember, reverse type (light type on a dark background) is much harder to read (it tends to “shimmer”). Those dark themes are handsome and sophisticated, but If you anticipate your posts will contain a lot of text, be kind to your readers and choose a light theme with dark type.
Background. What kind of background does the theme have? Is it a color, a pattern, or artwork? Different colors and patterns are usually available with the Customizer. Also check the theme’s appearance options to see what options might be available.
A variety of page templates. Many WordPress themes include a variety of page templates or layouts. It adds visual interest to have wide or full-width pages for big photographs, relatively narrow measures for easy reading of lots of text, and options to include or exclude sidebars. Some themes will expand to a full-width page if you drop all the sidebar widgets (either don’t use any widgets, or use their visibility options to hide them when you want a full-width page.
Image borders. Does the theme, by default, add a border to every image? You might not want borders on some images (eg., logos, irregular shapes, white or invisible backgrounds). Border defaults can be changed with CSS. Or you can add or delete borders using the image editor.
Captions. How does the theme treat captions? Does it include them inside the image’s border? Put them outside the border? Add a shaded background? Are the captions centered or aligned left? If you have strong preferences about captions, you’ll want to consider these things.
Block quotes. Do you like how the theme handles block quotes? Does it indent block quotes? Put a vertical bar along the left edge? Put a background color behind the entire block? (I’ve discovered those backgrounds don’t wrap around images.) Have a decorative quotation mark? (And is the mark correct or is it backwards? It’s backwards in Oxygen, for example.) The Expound theme hangs block quotes out in the left margin, which you may or may not like (I’m not a fan).
Infinite scroll. Do you like infinite scrolling, and does the theme offer it as an option, a requirement, or not at all? I’m not crazy about infinite scroll, probably because I worked so long in print publishing with finite pages. I generally like to have some widgets at the bottom so there’s less clutter in the sidebar(s). And I like my copyright line to show at the bottom of every page. That’s the customary location.
Comments. It doesn’t affect the look of your posts, per se, but do you like the way the theme handles comments? Does it put the avatars on the left or right, leave them square or make them round? Is it easy to follow nested comments and see whose comment is whose? And by the way, the theme should not require scrolling back to the top of the post in order see the comments or to add one. When you finish reading, the option to comment should be right there at the bottom of the post. Do you like the way the theme displays the number of comments? How prominent do you want that number to be and where do you want it to appear? Some themes display it prominently — in a big colored dot, for example — and others hide it in tiny type with the post’s metadata.
Return to home page. How does the theme return a reader to the home page? Does the header link to the home page? That’s the usual arrangement but not all themes work that way. However, you can always add a home page tab to the menu bar if you need to.
Menus and navigation. Do you like the menu display? Some themes have obvious menu bars across the top of the page; some have dropdown menus that are hidden until the reader clicks on an icon, usually the three-bar “hamburger” icon popularized on mobile devices. How many menus do you normally use and where do you like them to be located?
Archive (category) pages. Does the theme list just post titles on the archive pages? That doesn’t do a lot to draw the reader into those posts. Does it display the posts in full? That’s a waste of space, since the posts appear in full elsewhere, and it doesn’t utilize the opportunity to list a lot of posts. I prefer a theme that uses excerpts on its archive pages. That shows enough about each post to inform and tempt the reader, but still manages to show multiple posts on a page. Text-only excerpts serve this purpose, but some themes, like this one, include images with the excerpts, which I think is the most attractive, useful approach for archive pages.
Breadcrumbs. Do you like where and how a post’s tags and categories are displayed? Do you prefer them at the top, so readers can see them right away, or would you prefer them as more of an afterthought at the end of the post? Do they have icons with them and do you like the icons? I don’t mind a few categories showing at the top of a post, but I don’t want my title overwhelmed by a mass of categories and tags. Personally, I’d rather they appear at the end so they don’t compete with my title. I find most of the icons visually distracting and would prefer a theme not include them.
CSS. There’s virtually no limit to the changes you can make to a theme if you buy the customization upgrade. If a theme suits you and you just want to change some fonts or colors, it’s easy to do with the WordPress Customizer. If you are knowledgeable or feeling adventurous, you can change almost anything using CSS code. And with the premium themes, you can go to a theme-specific forum and get personal help directly from the theme’s designer.
Most important. Pick a theme, any theme, and start writing. It doesn’t matter what theme you’ve chosen if you don’t post anything.