I assume you mean sketch constraints. Unfortunately, this is a hard topic on which to provide any sort of generalized answer. Or, at least such answers are often opinion-based and may vary. You might be better off just coming here to the forum with more specific questions: How do I fully constrain this sketch? When I add this dimension, my sketch goes haywire. Then, over time, you kind of learn how do work with them. But, each person probably has their own method for constraining a sketch.
For me, there are things I stay away from: Sketch patterns, (unless the instance count is very low), equal constraint (no good reason other than I probably had a bad experience once with them, and so I tend to use dimensions and equations to make things the same length now). I tend to dimension line-to-line instead of point to point where I can, etc. These are partly just habits, and partly my experience.
To find out what is under-constrained, I tend to find blue geometry and try to drag it. That often reveals degrees of freedom in the sketch, and can help me figure out whether I need a dimension or a geometric constraint.
Jeff Strater
Engineering Director