First things first: If you have a shitty microphone than buy a new one (sm57 is cheap and very versitile). If you like to record spend a good chunk of money on a mic as they are THE most important part of getting good recordings.
That being said here are some really basic guidelines I've read along with my own thoughts:
1. Record everything "dry" meaning don't add any effects, eq, or anything like that. The exception would be some light compression. Once you have it recorded you can add all the stuff with software.
2. Place your mic about 3ft from your git pointed at the 14th fret. You can angle it towards or away from the soundhole depending on how much bass/treble you want this also will determine how much right or left hand nuances are picked up. Get someone to listen and find a "sweetspot" if you can. A lot of this comes down to experimentation. You really want to avoid pointing your mic directly at the soundhole though.
3. For the love of God, if your recording vocals get a pop filter! This will get rid of the pops that rear their head when you say 'p' words. If you have the scratch they can be bought for like $25 bucks but I made one with some panty hose and a coat hanger.
4. The room your recording in will have a big affect on the sound you get. Use your ears and find a place that sounds good or creates the affect your going for i.e. hardwood floors will sound different than carpet.
5. Vocals and guitar should be recorded seperately. You can do both to build live chops but sound quality will suffter.
6. Be conservative with reverb/delay but don't avoid it completely.
7. Be conservative with E.Q. but dont avoid it completely.
8. If you can, have your equipment set up and ready to go at all times. More importantly, when inspiration strikes don't waste any time! Get to your mic and PLAY. I can't tell you how many times I've thought of something and put recording it off then 24 hrs. later it's gone.
9. If YOU think your recording is bad than don't post it or play it for people. Take the time to do it right and then share it. If it could have been 100 times better with a bit more work than why have us critique it? Save the rough drafts for your own study. Btw-This is my main frustration with this forum.
10. If your singing you can vary your distance from the mic to even out the sound i.e. when you yell get farther away and vice versa.
Thats about all I want to write at the moment but theres obviously a lot more to it.
I didn't give any specific settings for compression/e.q./delay etc. because it varys too much. If you want some guideling go
here