Beginners often wear regular shorts (not short shorts) and a spaghetti strap shirt.  Yoga wear is very popular for all fitness levels.  As you advance you will need a bra top that bares the middle section to improve your grip, but it is not necessary in the beginning or parts of the intermediate levels.

The best pole dance clothing will be breathable and tight fitting.  Shorts should hug the bottoms of the buttocks, unless you want a "cheeky" look.  cheeky looks to help the grip in some pole moves but too much cheek is prohibited in pole competitions and isn't necessary at all for Pole Fitness reasons.  My favorite line of pole fitness clothing can be found here =>