Lenses - the pitfalls
When using a telephoto you should realize that depth of field is very shallow at wide apertures. Focusing therefore becomes very critical if you want your subject to appear sharp in the picture. Wide angles are much less critical in this respect since even at wide apertures their depth of field is much larger.
Camerashake can be a problem when using tele lenses. The rule is to use a shutter speed equivalent to the lens' focal length. So a 200 mm lens would need a shutter speed of about 1/250 to be on the safe side. With a wide angle of 35 mm however, it would still be possible to get sharp images at 1/30.
Since wide angles open up perspective they should not be used for close up portraits as the facial features of a person will be distorted beyond recognition and you can be sure you won't make many friends this way.
When photographing buildings or large objects with wide-angle lenses it is tempting to tilt the camera backward to include everything in the image. This will cause vertical lines to converge and it seems as if the building is falling backwards. If you want to capture architecture without distortion, step back a few meters or try finding a higher viewpoint.