>>6179429That's a good general tip, but even then it's tricky and subjective. Look at Bandai themselves, the differences between the MG 2.0, Origin, OYW and the 3.0 are immense. It's just about what looks good to you, and what you can achieve.
I'm not an expert or anything, but I always try using mechanical pencil first on an assembled plastic kit, or trying things out in MS paint over the top of photos of the kit. I also look at, but never SAVE other customs of the design, so that I can notice things I like, but not copy them. Most of the time though, I don't look at anything.