In general it is better to allow a blister to do it's own thing. The fluid inside is sterile and pads the injury. So if you can stand it, don't pop the blister.
If you must pop the blister, keeping the blister skin intact is important. So follow the advice given to pierce it with small holes along the edge using a sterile needle. Keep those holes covered with sterile dressings and antibiotic ointment as well.
Another method I've seen that works well is to use a curved suture needle with suture material. Thread the suture through the blister, this allows fluid to wick out of the blister. Cut the thread from the needle and discard the needle. Use only sterile, sealed suture kits. This is best done at night and allows the blisters to drain all night and prevents the holes from sealing shut. Remove the suture thread when you wake up in the morning as they would be irritating to walk on and could make matters worse.
If the blister tears open on it's own, you can protect it by sealing it shut again with super glue.
Deep blisters should be well protected with sterile dressing to prevent infection.
Blisters on the hands frequently tear open before you even notice they are there. Remove the excess skin and protect the sore for a few days.