AT64 ds is pretty marginal. You could open it on the button to be sure or complete in the sb after a couple of loose limpers but you don't want to be opening this hand UTG in a six max game. In general you want high cards, hands that have four cards working together and suited or double suitedness is a nice plus as well.

Also helpful is the OddsOracle Simulator from PPT: http://www.propokertools.com/simulations

choose your game
put in your hand
hit the rank button
...and play around

you find the documentation here

cheers for the help lads appreciate it

As plolearnerguy has said it, it depends on which position you are.
On small blind, Bigblind, UTG this hand does not stand much heat postflop.

Strong hands are hands, that hit the board postflop in multiple ways. With AA76 double suited or AQJT double suited are good examples where you can hit, set, flushdraws, straightdraws or all those combined.

Marginal hands are hands that only flop in a single way like KK73 without a suit. It can only flop a set to be strong.

Strong hands are also situational. So for example KK67 ds is a strong hand, but against an opponent that is very likely to have aces, it is a weak hand. Same with AQJT one suit. 8754 is a marginal hand but you would much rather have it against aces than either of those hands.