For the first couple of projects, stick with very simple designs. The 4 patch block and the 9 patch block are easy to cut and can make very nice quilts. Here is my advice:
1. Stick with one brand of ruler as much as possible. Different mfgs. have different markings. (I prefer OMNI brand)
2. PRACTICE, PRACTICE, PRACTICE accurate cutting
3. Make your iron an extension of your arm. Startch is a wonderful tool (IMO) but learn to press
4. Always measure your 1/4" seam.
5. Use "neutral" thread for piecing, off white, light gray, taupe. I use Maxi Lock thread for piecing
I can probably come up with more stuff but right now I'm drawing a blank. But the MOST important thing to remember is.............................BREATHE!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!
Don't be hard on yourself. Making quilts is to be ENJOYED. If you make a mistake, learn from it and move on. You might want to look at a book by Eleanor Burns DOUBLE IRISH CHAIN. Beautiful quilt and very simple to make and she gives you step by step instructions including which way to press your seams for easy match up.
Good luck and enjoy!