1. I would say the answer is it depends onthe situation.
Is it the first hand, you always getthe odd nutters who go all in with anything and hope to double /treble up quickly ( this happens every freeroll i've ever played).
Is it the first time they have gone all in and you are several hands into the tourney. They could well be sitting on a big Ace or pocket pair and again hope someone will call so that they can double up quickly.If so its best to have a premium hand if you are going to call.
Have they been doing this regularly? if they have, they have any two cards and so you could widen your calling range BUT you really need to be in late position if you widen your range. The nutter may be playing any two cards , but you are likely to be stuffed if someone after you shows up with a premium hand and you going all in will make the pot even more attractive to them.

2. pay attention during the tourney in hands you are not in , if people are minbetting the flop see what they had if it goes to show down and make a note of it.It will help you when you get involved in a hand when you are faced with this situation.Also what do they do on turn and river.

3. Can also depend on relative stack sizes and blind sizes and tournament stage. If you're very short stacked and soon to be blinded you should be in push fold mode and this would have to be a push hand.Good for stealing the blinds in late position.

4.see if you can see cheap flop and hit a big hand , The trouble is that you could end up just heamorrhaging chips . If you have a big stack then you could perhaps try seeing a few , but short sacked its a gamble and you really need to keep all the chips you can for premium hands that come your way.