first, apply a tight revoultion of making tape around the bottom of the carto (not the threads) this will hold the carto in the punch snugly and also prevent too much deformation.
to line up the hole in the correct spot, hold the bottom tank cap next to the carto. make a dot on your masking tape where the cap ends.
punch the hole by listening for the pop, like mentioned above. after you hear the pop, make another 1/2 to 1 and a 1/2 more turns, depending on how large you want the hole. for me, i go with 1 more full revoultion on the first hole, and then i make another hole with only 1/2 addition revoultion after the pop.
my juices are 65/35 for the most part and they wick well with this method.
another tip to assembling your IB Tank si to lube the orings and the carto as well with ejuice. the o-rings from IB are nice and snug, but can be a real pain to install when brand new without some adequate lube.
also, get a tank filling funnel, or a slap-yo-mama type device like the one sold at IBTanked. it not only helps with filling, but it protects your o-rings from the sharp edges of the carto.