A good strategy is avoid the box store bikes like Roadmasters etc. Often they didn't function well even when new. Silk purse/sows ear.
It's hard to build self confidence and ability when you work on a bike that nobody can make perform well without a major parts upgrade of the entire drive train.
Look for stickers on the frame that state Cr-Mo (chrome moly) steel and butted tubing. They will be above the bottom feeder level with the other parts having a higher level of functionality. IOW, repairable.