A long post but words on gameplay....
Reduce the gravity a bit so you can jump higher than normal to look for spots where some people will use jump tricks to get to glitch areas. And always approach it with the assumption that even though some action sounds silly to you or that players would never do it... they will. Always. ?
Now is the time before spending a whole lot of effort in the editor to decide whether you want a specific type of gameplay that favors certain styles and weapons or a more balanced one (my preference). Little things can have huge impacts.
Include three ways to exit spawn areas to cut down on unfair spawn trapping. Make sure spawn points are reasonably protected to prevent campers zoomed in from a distance waiting for players to pop in. Not every mod has spawn protection.
At least three general pathways to get to enemy areas. Its common to have one open path in the middle and a CQ path on each side (Crossfire) or some other combination (Overgrown/Farm). If its a small map make the pathways take roundabout routes, or many obstacles, so its not a straight shot from A to B nor too quick to get there (Combat Medic / Lightweight). This is especially true if you want it to work with CTF or other objective games.
Camping and snipping are valid play styles so dont want to prevent them but dont make it too easy. Yes thats a no-brainer but mappers can come with their own biases and give advantages towards their own style of play. Someone may detest snipers but it must still be just as fair to them as others. Rushers should be vulnerable to explosives but make it difficult. Teamwork and pushing should be encouraged by allowing good defenses along the way.
Most general areas should be open to attack from at least two directions, either by direct player fire or grenades. Objective points are a bit of an exception and the two team objectives should require attacks from close range and hidden from view at long range. The center objective should be open (Convoy etc) so it is heavily fought over.
And then... its your map and you are not going to make everybody happy. Some are going to complain that it sucks because it cramps their style and doesnt give them what they want. The logic: "My K/D isnt good compared to other maps therefore it is bad". Save yourself the grief and good gameplay comes first always.