A good self-tape is easy to watch, follows the instructions, and makes the scene clear. Clean sound, simple light, a stable frame, and a prepared reader create the conditions. Specific acting does the rest.
Frame the shot as requested and keep the eyeline close enough to camera that we can read your thoughts without feeling that you are speaking to the lens. Make sure the reader gives you something to work with instead of racing through cues. Do not cut around the scene so tightly that the moment before and after disappear. Watch one playback for technical problems and story clarity, not to punish every small movement. Ask: can we hear it, can we see it, do I know what this person wants, and does the other character affect them? If yes, submit the work before endless retakes sand off what was alive.