It helps to play the game a lot to understand it, and in games like CS to try to at least watch some competitive matches since competitive players tend to focus on the most efficient and advantageous parts of the maps.
Regarding CS defuse maps this article sums the basic layout http://www.egir.dk/index.php?page=vhe_layout.htm if you understand that you can change it to make yours more unique like for example on de_nuke where the bombsites are on top of each other
Besides that you need to take into account the timings of the map, how much time it takes each team to reach the chokepoints and bombsites, if Ts can switch sites fast enough to make a fake, if CTs can get to each bombsite after the bomb plant with enough time to retake and make the defuse, etc. It seems like nowadays smaller maps are preferred due to those timings being smaller making the games faster, that's somethoing that you can play with as well.
Finally you need to take into consideration each type of weapon, that is you need to have separate sections that favour long, medium, or short range weapons. You can solve this by looking at the lines of sight in the map, that is how much of the map the player can see in a certain point, long lines of sight help snipers more than rifle players, and tight areas are better for pistols and smgs. So ideally you want two or three areas with long lines of sight for awpers, another two or three that are more cramped like small corridors and stuff like that to help in pistol rounds and have the rest of the map with average lines of sight for rifles action.
Hope this helps.