How to keep the best quality on a video?

I have a nikon d5100 and i have been making some videos. The file type is a mov which i edit on adobe premiere pro cs3. However when i put them onto adobe, the quality of the file is considerably reduced and as i render the movie and export it, it gets even worse. I transfer the data from memory card and copy it onto my computer. What am i doing wrong? Do i need to convert the video files somehow? Please tell me as i have edited the film up great!

You're Exporting The Movie Either Too Fast, Or You're Exporting It With Bad Settings

It depends on your video itself, adobe premiere cs3 is the best video tool

You are shooting H.264 video files in 1080p 24fps I take it. I would try exporting it as the same thing you brought it as. Every time you transcode footage you will loose some quality so the best be is to work in the most uncompressed format you possibly can then we it comes to the final video compress it to the format of your choosing.

Remember GIGI (Garbage in, Garbage out)