Very simple, but I always seem to forget the format:

tar -cvvf name.tar dir/ --exclude dir_to_exclude directory

You actually need to use the full path and sometimes swap the order:

tar -cvf name.tar --exclude "/full/path/dir/exclude_this"  /full/path/dir/

Here’s a couple more tar commands for good measure:

tar -cvvf file.tar file.txt (tar file)
tar -cvvf file.tar home/ (tar dir)
tar -xvvf file.tar (untar)
tar -xvf  file.tar (view)
tar -cvvf archives/20040918.tar *php *txt (example)