Alright, I'm no professional with mapping, but I'll try and go over what I try and do with them.
With capture point locations (depending on if it's AD, 5CP, or KOTH), you need to think about a few different factors: is it easily visible; is it easy to get to; how hard is it to defend. All these things matter when deciding a location, as well as balancing around an already decided location. I mostly know this because my A1 of Nightflower had a horrible, horrible issue with the point not only being hard to find, but also was super inconvenient to leave from.
If your capture zone is too big or too small, it can make things pretty rough to deal with. I personally think that having about a 512Hu by 512Hu capture zone is pretty consistent size for most capture point locations. Again, with Nightflower, since the point is in such a weird location, I decided to make the point a bit bigger to make up for a lack of high ground.
I'm no professional, believe me on this one. Other people will probably give much better advice due to experience and practice. If I had to recommend a video that somewhat helped me with figuring out my control point issues, I'd say Red Robot's "What makes a mid good?" video is a pretty decent guide to why certain control points work as well as they do.