As noted above, starting with at least one of the top 3 high or low spades in the hole gives you a better chance at winning. Without a good spade in the hole your only possibility of winning requires that you make both the best high and low hands. That's a tough spot to be in, since you are going to have to stay in for up to 5 rounds of betting before you know.
when you are not dealt at least 1 spade as one of your original 2 hole cards you should consider folding unless your original 3 cards give you an excellent shot at drawing the best high and low hands. (For example 3 suited low cards or 3 low cards to a straight.) While it may still be possible to pick up a winning spade as your last hole card, there are too many rounds of betting you will have to weather and too small a chance of doing so. In the very best case scenario - 7 players staying until the end and neither the ace nor deuce of spades appearing among the up cards - there is only about an 9% chance of you catching one of them as your final hole card. The more likely case is that the winning spades are already among your opponents hole cards (why else are they in?) and you have zero chance.
You should also consider folding if you are dealt only a middling spade such as 7, 8, 9 (probably 6 & 10, too) and don't also have a very good start for the high or low hand.
The absolute best starting hand you could get is ace of spades and deuce of spades as your 2 initial hole cards. You are now certain of at least a tie and virtually guaranteed to win. Your only concern would be to keep as many players in the game as possible and build the pot as high as you can. Having both a high spade (K♠ or Q♠) and a low spade (3♠ or 4♠) while not a lock, is worth playing. Obviously, you'd love to see any higher or lower spades show in the up cards. Another excellent starting hand would be trip aces with the ace of spades a hole card. You are half way to a lock and you have a great chance of making the best poker hand.
Having either the ace or deuce is a much more achievable 12:1 chance and is certainly playable. Now you are hoping to develop the highest or lowest poker hand or catch another winning spade as your last hole card. You could even win if no other player has a spade in the hole as a single spade in the hole can be considered both the highest and lowest in play. You'd prefer it to be the ace since it can act as both a high and low card, while the deuce probably only helps your low hand chances. Consider coming out strong right away in an effort to eliminate players which will give you a better chance of ending up with the best high or low hand.
It is about a 16:1 shot of both of your original 2 hole cards being spades. If they are both middle ranked and you have no other draws it is usually best to get out right away. But, if you are starting with 3 to a flush or straight or a pair with a high kicker, it may be worthwhile to play and see another card or 2.