From a technical point of view, please don't try and make one without a decent capture card. Make sure the audio quality is also good. From a directing point of view, make sure you don't use crappy camera angles. Do not use much "moving cameras", always have the camera stationary unless you are doing some type of action scene. From a acting point of view, make sure your voice actors aren't horrible. They don't need to be the best in the world but they need to at least seem like they aren't reading from a script. From a writing point of view, there are many things. Don't make the plot too confusing, especially for a first time. If it is a action machinima avoid using generic lingo like "delta squad alpha roger roger" or whatever. It makes it feel tacky. Focus on a set of characters; don't just focus on a battle or something. Likeable characters are key. If it is comedy please make sure it is actually funny.