Lighting - it's very important as one might guess. Too little, and you really can't see the subject. Too much and you wash your subject out. Sometimes, you just don't have a flash to give you that extra oompf or you realize that the flash is too bright and you don't have a diffuser. If all you have is an on camera flash and you think it's too bright, tape a single or double layer of napkin or tissue over the flash to soften it. Looks goofy, but it works. You can also make reflectors using index cards and tape. Just make sure those paper items are white, white, white. Translucent plastic work as well.
If you have access to natural light - on the balcony or outside on the street, you may find it too bright and your subject may be too dark or get washed out. Either get your subject to a shaded area and reflect light onto them or place either an opaque or translucent barrier between your subject and the light. You can also do both - block light and reflect other light depending on the effects you want.
Don't have a fancy set of reflectors? Position somebody that's wearing a white, silver or gold-colored t-shirt, cosplay costume, or even use a white paper plate or sheet of white paper. I understand that tungsten or fluorescent light inside may not work as well, so try to manipulate it as best you can. Of course, you may just happen upon a scene that you won't be able to adjust light for. Shoot anyway and use iPhoto, GIMP, picasa or noise ninja (or both) later if you need to. If you have a compact digital like a Canon G-11, Nikon P7000, or PEN, you can set your white balance (like a dSLR) and play with the outcome
If you are one of those shooters that has one or more strobes that you can remote (using Nikon CLS, Canon's version of that, or pocket wizards), there are probably bystanders willing to be your voice-activated light stands.
The best thing to have with you? A friendly, non-threatening demeanor (meaning don't be creepy) and polite manner when asking to take someone's picture. Remember to say "thank you"! If you plan on posting any image, make sure your subject is okay with it and tell them where you will be placing it if they have no objections. I will tell my subjects where they can find it, usually on deviantart or flickr ( i try to have buciness cards with me) and let them know that if they want a full up 300 ppi image, to ask for it, providing me with details related to the time that I shot the image.
Megapixels and photo size, just so you'll know -
This website can explain what is what so you can determine how large you can blow an image up to.
Post-production Photoprocessing for free -
Can't afford Lightroom, Aperture, or Photoshop? Use picasa or GIMP. There are versions for PC and MAC both. And as indicated, they are free and can do most of what people shooting happy snaps need done.
Edited by Gremlich, 05 March 2011 - 04:24 PM.