Let's run through the things that give a site that professional touch.
Unlike designing a regular web site, where you're basically starting with a blank slate, the great thing about WordPress and its themes is that your site can instantly look polished and professional — or whatever look you're trying to achieve. You'll probably download and try a bunch of themes at first, maybe call a friend or two and have them do a 'Refresh' as you switch the themes and get their opinion, and eventually you'll settle on the one you want.
Balance & Symmetry
You'll notice that most professional sites use roughly the same proportions when it comes to their banners, sidebars, columns and footers (if any). If the theme you've picked is a little out of balance, grab the bull by the horns and head for the dreaded 'Theme tweaks' page. It might be nothing more than changing a "325" to "225" and bingo, the width of your column looks perfect. Ditto the width of the text area, height of the banner, footer, etc.
This deserves some consideration. People out there in blogland are savvy enough to recognize an out-of-the-box look, and they'll figure if you can't even put a little effort into making the site 'yours', what kind of effort are you going to put into your writing? What makes you different than the next out-of-the-box joker to come along?
So, if you have a picture or banner with the site's name in it somewhere on the home page, grab little Color Picker and make your header fonts and/or sidebar fonts the same color, or a derivation thereof. Make your site unique.
Notice the colors in the following "blockquote":
There are three types of people in the world:
Those who makes things happen, those who watch things happen, and those who wonder what happened.
Notice how they match the sidebar. If you're really trying to convey to people that they're on your site, these little things add up.
The general rule in the desktop publishing world is "no more than two font styles per page", excluding banners and the like. It's not uncommon to see four or five styles on one blog, giving it a decidedly unprofessional look.
What you'll do is have one basic font for all text, then have small sub-rules for specific instances, like headers:
always underlined, or
always bold, or
Ditto your use of colors. If you use them in one particular circumstance, always use them in that circumstance, and stick to the exact same colors.
And please do NOT use gray-ish fonts. A surprising number of themes out there have light gray fonts, rather than dark gray or black. Sure, it looks real snazzy and modern — but everything's harder to read! A classic case of "putting fashion before function."
Also, you'll want to consider whether to 'block justify' your paragraphs; meaning, the lines are stretched out so there's a neat border along the right-hand margin, like this site. I'd say if the site's on more-or-less a 'professional' level, then it looks good. If you were going for more of the individual shoot-from-the-hip approach, then it would look corny and pretentious.
The font style is also strictly dealer's choice. Personally, I've always thought Verdana is easier to read than Arial, but Arial is what's caught on in general, and that's what this is.
What you might do is make up some mock 'readability' tests and see what looks best on your site. Take a couple of big paragraphs and make them one font, then duplicate the paragraphs and do the same with the other fonts. Then make another block Bold and one block not, and then ask some friends what they think. For a fun, happy-go-lucky look, the 'Comic Sans MS' font is kind of cool.
Every pic you put on the site should already be the correct size before you upload it. The algorithm a commercial image editor uses to resize a picture is far, far superior to the one in the browser. If you put a 600 x 600 pic on the site but reduce it down to 300 x 300 so it fits next to your article, the viewer's browser is going to make the conversion and it's not going to do as good a job as a real image studio, even humble 'Paint'. So you always want to get it the right size first, then post it.
Also, you should do some experimenting with your particular theme and see how wide you can make your pictures before they expand too far on a standard 1024 x 768 monitor. Width-wise, you should know what your maximum 'big' picture can be. If it starts pushing things beyond the right side of the browser or the sideways slide gadget suddenly pops up down at the bottom, you've gone too far.
Using a hidden table is the proper way to list things. Line up a list of items using the 'Center' command and you get:
Cherries = $1.29/lb
Lettuce = $1.33/lb
Tomatoes = $1.34/lb
Apples = $1.48/lb
Corn = $1.98/lb
But with a hidden table:
With the border lines:
One more note about tables: If you want the columns to be a certain width, click on a cell with the right mouse button and open 'Cell', 'Cell Properties'. For example, if you had four columns and wanted them all to be the same width, change one cell from each column to read 'Percent' and '25' for the width.
To Typo Or Not To Typo
That is the question. Some bloggers take the professional approach and if they spot a typo or outright mistake later on, they'll fix it without any notation. Other bloggers take the "real me" approach and if the 'real you' can't spell worth beans and makes stoopit spelink mixtakes, well, that's life. The way they view it, once you hit the 'Publish' button, it's set in stone. Then, should they ever change anything in a post (horrors!), they immediately notate it at the bottom of the article and hope the readers will understand their heinous breach of protocol.
As perhaps is slightly obvious, I lean toward the former approach. I fix a mistake as soon as I spot it and can't understand why I should mention it to anybody. But, on the flip side, there's no doubt that if you're going for that real-me 'air of authenticity', a bunch of blatant spelling errors will certainly help convey the message.
This is a tough call, because you're teetering between 'professionalism', which means not cussing, and "being yourself" by writing as the 'real you'. Either way, you're going to get criticized by a certain segment of your readers. If you keep it professional, you'll be accused of "not being a real blogger." If you swear up a storm and let it all hang out, don't be surprised if the commentary borders on the moronic because your more educated readers have moved elsewhere.
So, part of the answer stems from within, and how you, yourself, want to portray your persona to the world, another part comes from how you want your readers to react to said persona, and a third part comes from what kind of readers you want. So, you'd better make some hard and fast rules right from the get-go when it comes to language, both for you and the commentariat.
If you're starting a political blog, then whichever ideology you lean toward will determine your language to some extent. As a general rule, conservatives don't swear because it shows a lack of education and liberals cuss up a storm because it shows passion for their cause. Deviate from that path at your peril.
If you're going to keep the site professional and basically cuss-free, there should be some kind of "By commenting on this site I agree to the site terms…" notice in the comments area and a link to a "Site Policy" post so some commenter can't later claim "But I didn't know!" when he issues a huge string of vile racist slurs and you ban his sorry ass.
In my own writings, I'll use the occasional "hell" or "damn" if the situation fits, but nothing worse. Both of those might be used in a Time Magazine or New York Times article and not be deemed 'unprofessional', but step across the line much further than that and you might as well just slap on your renegade pirate's hat and go for it.