Yet another long-winded response I wrote, turned into a webpage. Convieniently enough, the title was "How To Take Pictures?", and knowing a little something about pictures (I only have 568 images on my website at this time), I offered my advice. The scope of this page covers photography in regards to images on the web.
If your camera can't focus on anything very close, then Don't Try! I can't emphasize this enough: countless times I have seen pictures ignorantly taken way too close, destroying all useful information that the photographer actually wanted to show! If you can't get close, don't. The best results are always at the focal length. Some cameras can focus very closely (my Canon S1 IS can get within a few inches, which is as good or better than my own eyes), while cheapos may have only two focus settings, "infinity" (practically, probably more like >4ft) and macro (maybe 6-18").
Good lighting is necessary. Some cameras do better in dark conditions than others, but you still need to enhance the image afterwards. You always get better results (sharper, not as grainy) in bright conditions.
It's a good plan to frame your subject as large as possible, to maximize pixels. If you have a narrow subject and optical zoom, by all means use it! If you get close to an object, so it fills a wide angle of the lens, it will get distorted. I haven't met a camera that doesn't have this spherical abberation. By using optical zoom, you keep the subject at high resolution, yet a low angle in the lens. This makes flat objects appear flatter and straight lines straighter. It also reduces perspective (the image covers a smaller region around the vanishing point), which you may or may not want in your photograph. I used this to maximize the area and minimize distortion while photographing triode plate curves, which I did by mounting the camera on a tripod aimed square to the oscilloscope CRT. (A significant amount of image editing and line drawing -- with merely Windows Paint -- produced the plots shown.)
After you take the picture, you inevitably need to tweak it. This is very easy today with pervasive digital cameras, yet I'm astounded by the lack of skill shown daily on the internet! Here are some tips:
Cropping is important, and too many images I see are oversized because the photographer didn't consider what in the image is actually useful information. If you're going to take a picture, why waste space on background? I usually frame the subject in, oh, 80% of the image's width and height I would guess.
Formatting is another consideration. If you are putting an image in a sidebar, flowing text around it, a reduced size would be a good idea, somewhere around 200-300 pixels. If you want to flow text around it while preserving a higher resolution copy, you can use a thumbnail and hyperlink it to the bigger image. I do that on occasion. If you put the image inline between paragraphs, then full size would be better. I have examples of all of these on my website. In the interests of resolution, I've mostly been doing inline images lately, around 500-800 pixels in width. Here are examples of both: Scope Mod: an unusual example, as the images are rather large for placing along the sides. I felt like putting the first three images to alternating sides, partly because they are taller than they are wide (putting them inline would be very tall, and placing them in a row, side-by-side wouldn't allow me to talk about them in sequence), and they are much, much smaller than the images they hyperlink to (in fact, those links are the three largest images on my entire website). Partly because I had a crappy camera for the first year, I made a lot of smaller images, and I liked the whole sidebar type presentation, such as here: Furnaces.
Most of the images on my site are 10-50k, averaging 20k. The whole site (including HTML) only takes up a bit over 10MB. It's compact, fast to download, and I think it gives excellent results in the simple style of HTML that I write.