This is best done in a pub where you will find all of the required materials:
1 Fairly flat table
1 Pint of beer (preferably half full)
1 match
1 beer mat
1 set of half drunk mates and preferably a pub

Okay here's how it goes: Place the beer mat on the table and the match on the table along the left hand side of the beer mat .

Place the pint to the left of the match and, keeping part of the glass touching the table, tilt the glass to the left.

Whilst tilting it, push the beermat (and match) using your right hand under the pint glass until the match touches the base of the glass.
Now holding the beer mat in place, tilt the glass back and forth until it balances against the match without having to hold it (this takes some practice).
Then pull the beer mat away with your right hand and wave it under the pint glass which appears to be balancing all on its own....magic !
Done properly, by wetting the bottom of the pint glass, the match will stick to it and you can lift it up and the match will come up with it.
Be warned though, the night could be totally ruined if the person you have been trying to get a date with for the last two weeks is facing the open end of the glass when it all goes horribly wrong.

People nudging the table will make this trick completely impossible and a steady hand is useful.   Have fun !!