All the above advice is good but to summarize:
1) Most DSLR cameras have a manual or "M" focus setting, so consider using that when there is this kind of issue.
2) Most DSLR cameras have at least three default focusing settings. One is the typical point it and shoot and the camera will do the rest. Another pinpoints (center focusing) for focusing and the third allows you to frame your shot yet move the focusing point. This is great for those tripod shots.
3) Most cameras allow you to point it at your subject and hold the focus by pressing down lightly on the button, and then (after you move the camera to frame the shot) press all the way down to take the shot.
4) Rarely a prime lens needs "tuning", and I don't think that is your issue. Some modern DSLR cameras allow you to adjust for front or back focusing lenses, but again this is rare.
5) Depth of field is a biggie when taking good photos, and articles on this subject and DoF charts can be found all over the Internet. A quality lens may cost more because it allows for a greater out of focus blur (bokeh) and is still sharp wide open. Sometimes you want everthing sharp, and sometimes you want the background blurred. That is why newpaper and sports photograpy is often times subject sharp and background blurred.
Below are two handheld shots, both using the "center focus" option. On the first shot I simply pushed the shutter release button half way down until I heard a beep (meaning it was in focus), framed the shot holding the button half way down, and then took the photo. In the first photo the background is an ugly chicken wire fence so it was shot wide open to blur the background. If I had a longer lens with me you wouldn't see the chiken wire, but that wasn't the case. The second shot needed two subjects in focus, while trying to blur the background so it was shot two stops from wide open (by my son for a scouting merit badge). Neither of these are "money" shots, but they are examples of the above and suitable for our purposes.
Last idea: Go to www.500px.com and "search" for the type of photo you are trying to take (e.g., "stars streaking" or "fireworks" or "flowers", etc. Then find some photos you are crazy about and see what shutter speed and aperature the photographer used. 500px is a great learning tool for me.
Edited by quant2325 - 8/28/12 at 10:09am