Hi, if they are moulded doors then dont go to mad on the paint and just check the corners where paint collects, if it starts running just gently dab your brush on the run, if there flush doors id suggest a 4" roller (foam one) and just load the roller and roll it on you will get lines but roll over them gently and they will go, sometimes you will see little bubbles come up but they do go so dont panic, but like others say getting a decorator to do them is advised if you want a good finish and you dont think you can do it.
cheers
steve
Oh and dont use a cheap gloss, use quality product for good finishes