1. your hand is very strong; a set certainly would qualify.
2. you will probably get everyone to fold out by betting; this is important: if there is an ace on the flop, there is probably no need to slowplay-- if tp isn't going anywhere, just build the pot.
3. the free card has good possibility to help make a second best hand
4. free card has only a small chance of outdrawing you. Also key-- slowplay on draw heavy flops at your own peril.
5. the pot is not very big-- often overlooked: if the pot is big you should be looking to take it down.
Even sets I would not slowplay very often. A set of 2 on a board with high suited cards can be deadly. On rags, it'll be easier to slowplay if you are first to act against agressive players. And the agression factor needs to be high for a slowplay to be effective, against calling station, I bet hard trying to represent a semi-weak hand trying to take it down now (TpNK, etc.).
I slowplayed Aces PREFLOP for the first time in 4 months today. The table was very tight and would fold to ANY raise unless they had a strong Ace of suited paint cards so I limped in the CO. Pot went three-way and everyone caught something, especially me for a set. With two flushed cards, I bet 2/3 and bam, raise and reraise. I pushed and caught another ace on the TURN! Woohoo!