Contrary to popular belief, sometimes it is okay to reach a total of more than thirteen tricks during the bidding. This is only true, though, if both oppopnents have overbid thier hands. The reasons for this become a bit complicated when trying to figure out if they in fact have overbid. So, how do you tell?
Apart from knowing your own partner's bidding habits, if he/she bids reletively low, say 1,2, or 3, and the count to you (as dealer) has reached higher than your certain tricks would allow (for instance, the count to you is twelve and you know you can take two - because you have a singleton or a void, along with the Ace of Spades), then bid what you know you can take. The danger in this is if your partner has overbid his/her own hand. But, you have no way of knowing this. The benefit of bidding sure tricks even if the count goes to fourteen or more, is that if your side makes their bid, not only do your opponents go set, you do not get penalized with overtricks!
As with any "rule" when it comes to bidding, caution should be used when employing this strategy. It is better to underbid once in a while and avoid the 100 point penalty; but too much underbidding can cost you the game. So which is better? I personally prefer to underbid in order to set the opponents as much as possible - then when they are two hundred or more behind, it doesn't hurt that much when my side reaches ten sandbags...for we are still ahead.
Another tip for bidding hands: how do you know how much to bid in the first place? One great method is to count (in the non-trump suits) Aces (one each); Kings (with two other cards as one, with two other cards as one but with three or more other cards as nothing, (because the likelyhood that someone has a singleton in the suit is greater the more cards in that suit you have). Queens are one only if you have two other cards. Any more and someone will trunp that suit before your queen comes out. A void is worth three ( unless someone bids really high before you, a singleton is two, a double is one. When an ace or a king is part of the singleton or doubleton, be careful you don't count things twice. Lets look at a few hands for examples:
1) You have the Ace and Ten of Spades, and no other spades in your hand. The ace is one but do not count the doubleton because this is the trump suit. You also have the King, eight and deuce of Diamonds. The King is one. You have the Ace of Clubs with no other clubs. The ace is one and because you are now out of that suit (when you play it) you can probably count two more for trumping it). The rest of your hand is a bunch of Hearts but the highest is only the Jack. Do not count anything in this suit. The total bid is 4.
2) Should you have two or at the most three trumps (the highest no higher than a Jack or more preferably the ten), and no aces ... a nill bid is in order. But a king, Queen combination is deadly to a nill hand unless you have at least four other low cards beneath them for it is conceivable that a suit can be led four or five times.
3) Should the bidding reach astronomical proportions before it gets to you, say thirteen or highewr already, double-blind nil is called for.
4) Hearts: Ace, three. Diamonds: King, Queen, nine, two. Clubs: Ace, ten, five, four. Spades king, ten, eight.
A/Hearts is one. Hearts doubleton is one. King of Diamonds is one and four cards keeps the queen from being counted. The Ace of Clubs is one. The king of Spades may or may not bring a trick (Only if the Ace comes out into play and you can play some other spade then will the king count but you do not know this will happen at this point). So the bid is: four or maybe five. If you are dfealer and the didding was eight before you, go ahead and make it five more. But be cautious during play to see if you can push out the Ace of spades by leading something someone elase is void in if you can. If you are relatively early in the bidding, say first or second, and the oppontnts are ahead of you, you might consider just bidding two or three, to trick them into overbidding. (Dealers like to keep the bid at thrirteen even if they can't make it).
If all this is complicated to you, just think Aces one each, with no other cards then it is a three, with one other card it is two. Kings are one. Queens are one only with two other cards. Singletons are two, voids are three (unless these two situations also have an ace or king in them, then reduce by one point for each).
And don't hate sandbags. They can be your friend. But I wouldn't be too free with them until you can bid accurately or learn to play so you don't get sandbags. That way, when the saandbag count reaches nine, hopefully you are ahead enough of the oppoments that they can't catch you and you can keep from hitting the dreaded ten count. But, as mentioned earlier, if you are far enough ahead, go ahead and get ten while they are behind. You will then be at zero again!