I'm not sure why this is difficult for you...
In the Edit View Scheme dialog, go to Step 4 and click the arrow on the far left of the Search Box. Choose Genre. In the dialog that appears, check the box for any Genres you'd like to exclude, and change the "Do what with the selections" option from Include to Exclude.
Or, you can just type it in manually. Prefixing a "-" to any search term in the search box will act as a NOT (exclude those results) for that term. Some examples:
-[Genre]=[Indie Rock]
-[File Type]=[mp3]
-[Keywords]=[]
(That bottom one excludes items with no keywords assigned.)
Regarding Jaguu's point above... Just find something that works for you, and you can design specific View Schemes to make navigation make more sense. For example...
For video, I use the Genre field to denote "type" (Movie, TV Show, Music Video, Comedy, etc). For my Movie files, I use Artist for the movie's director, Album isn't used. For TV Shows, I use Artist for the series title, and Album for the season. I then have two separate View Schemes under Video for viewing these file types...
One is called "Movies/Director" which contains:
Step 1: just Artist
Step 4:
[Media Type]=[Video] [Genre]=[Movie] ~sort=[Name]
The other is called "TV Show/Series/Season" and contains:
Step 1: Artist and Album
Step 4: [Media Type]=[Video] [Genre]=[TV Show] ~sort=[Artist],[Album],[Name]
If you don't want to do it this way, you could also define your own fields under Tools --> Options --> Library and actually call them "Director", "Series", "Season", etc. I don't just because it's easier to just use the existing fields. Re-using the fields also makes it easier to have "general" view schemes. I have a Genre/Artist/Album view scheme and a Genre/SubGenre view scheme (I created a SubGenre field which I use for both Audio and Video files) which show all of my video files and helps me when I'm tagging them...