What kind of source clips? AVCHD and other card-based formats need special handling for best results. Copy entire contents of SD card to hard drive, not just the "video" clips. Then use Media Browser in Premiere to do the Import. This solves a lot of issues with clip playback behavior.
For Export, "Max Render Quality" is only useful for scaling the video, meaning the export frame size is different from the source, like 1080 to 720, or HD to SD. Otherwise don't use it.
Usually, it's best to NOT "Use Previews" - these are not always the highest quality depending on which preview render codec is being used, and in any case, it means you've added another generation of compression - source clip to preview render to export file. Best to export direct from source (timeline). Unless parts of the timeline just won't play without rendering, I don't bother with rendering timeline to "green". Red doesn't hurt anything as long as timeline can still be played.
Frame Blending - this is only used when converting frame rate. Do NOT use this otherwise. Checking all the boxed arbitrarily just increases render times and in some cases hurts the quality.
For YouTube, are you using the YouTube preset found under H.264?
Thanks
Jeff Pulera
Safe Harbor Computers