The cracking/wrinkling could be due to a number of reasons, from incompatible paints and primers, bad temperature or humidity, or even not shaking the spray paint enough before applying (tip: for best results, skake the cans for several minutes).
About paint masking, that's easily Googled or just found on the internet. Generally, just masking tape and paper is used to mask off areas (hence the name). Again, for best results, there are some blue painters tapes that work even better. Also, do not use newspaper to mask. The ink will smear on the paint, especially if it's not 100% dried. Use brown paper rolls or even cut up brown paper bags.
To paint a stripe or detail piece, first you should know to always paint darker colors on top of lighter colors, never the other away around. Generally, just paint the entire pieces the base coat. If the detail color you want to use is lighter than the base coat, mask it off and spray with a white or gray primer, and then spray the detail color on that.
For small details, I generally make stencils, and sometimes you can simply hold them on by hand as you spray. Or, you could even purchase self-adhesive printer paper and print out your own personal or customized stickers for really small graphics or text. Don't forget that whatever you do, always spray a coat or two of clearcoat to seal everything.
