With medium and low pair. Simply call to see the flop or pre-flop raise a small amount that you can afford to lose. If the flop is favourable then conquer the pot.
In the early stages of sng never pre-flop all in raise cause chances are that some one might just have an overpair easily.
Towards the end of the tournament they greatly became reliable hands to steal blinds or for all in pre-flop in case you are short-stacked.
But in any case beware of your opponents since they can get and over pair very easily in case u don't secure a triple or full.
Regards
Bruno Costa