If your run is segmented, the segment transitions have to be smooth and somewhat seamless. Make sure the in-game sounds play out nicely throughout the transition, especially if there's in-game music playing.
Your run has to be very optimized. If you lose seconds here and there from sloppy BHopping/ABH'ing and/or your routes could easily be improved, your run will not be accepted.
Your run can not include any sort of copyrighted material what so ever. If a mod uses a licensed song for example, you need to either replace the music during that part or remove it completely. An example would be Still Alive in Portal which is played during credits. Simply replace it with an instrumental version and you're good.
Do not add any sort of editing special effects such as slow motion, motion blur, lens flares, etc. The only alterations of the game we approve that may be added in post production is the runner's name, end credits and color grading to smooth out segment transitions.
More on high-quality video production:http://wiki.sourceruns.org/wiki/GoldSrc_Video_Creationhttp://wiki.sourceruns.org/wiki/Source_Video_Creation