Avoid these common mistakes and you'll make better recordings:
Clipping. Digital clipping is awful and you can't fix it. Make sure your meters don't hit the red and you will have a much better sounding recording.
Recording At 16bit. We want all the headroom we can get. Use 24 bit audio with record meters peaking at around -12 to -10 db.
Recording Bad Instruments. If an instrument is faulty, out of tune or needs new strings or heads then replace them before you record.
Cheap Cables. Cables matter. If you hear some noise while recording chances are the cables are no good and this will end up in the recording. Check your cables and use quality cables.
Recording With Effects. It isn't necessary to record with effects into your DAW. By doing this you limit your sound to which ever effects are on those tracks when recording. After being mixed and gain staging those effects will be too much. If you do, use them subtly. Best bet, leave them off until after you've recorded. If you do, use them subtly.
Recording With The Wrong Microphone. There are 3 types of microphones Dynamic, Condenser & Ribbon. Selecting the correct mic can make the difference. Do a little research and read up on each microphone type.
Mic Position. Move the microphone around the room until you find the sweet spot. You will hear it and you will know when you've found it. Raise the mic stand, lower the mic stand or turn it. Experiment with the placement and you will notice improvement in your recordings.
Sound Treatment. Some sound treatment is better than none. Understanding the way audio waves travel and bounce off of things in the room will drastically improve your recordings.
I'll Fix it in the Mix. Don't be lazy with your recordings. If there is a problem with the take, do it again. Get it right before the mix, this will ensure that the mix brings out the best in the recordings.
Being Unaware of Rumble. Block out low-frequency noise it can completely destroy low-end definition, turning your recordings into mud. Use a high-pass filter and roll off the extreme low end.