A lot more complicated than you would think. You basically have to find things elsewhere and then apply that knowledge to the duel arena.
People will not tell you those kinds of glitches, after all why would they want it to end up getting patched sooner?
If you want to find one for yourself, read around about how people discover them in the first place. There are a few topics on here describing the exploits of a Bug Abuse team that stopped there "exploits" about a month ago.
Read descriptions, go try to find some CFT's/PAFT's/etc. and if you find them, never tell ANYONE how to do them (except me because you love me for telling you all this, right?) so you don't lose out on profits.