Opening Bid: One Diamond
This particular bid is probably the most frequent of all when you play a forcing club system; it is also the weak point of the bidding structure because it gives the responder almost no information other than the fact that his partner has an opening hand. It can be as short as a singleton. The point count is 11-16 HCP and should be alerted as, "May be short."
Because an opening call of 2 shows a hand with a 5-card diamond suit and no 4-card major, the 1 bid denies that holding. If the opener rebids the diamond suit he must also have an unspecified 4-card major, but one which is often revealed from the auction. Opener might also have four diamonds and five clubs, too, but responder will not know that until opener's second call.
Treat it as semi-forcing. You can pass with a weak hand, but only if you have at least four diamonds. If you don't have that many, even with zero points, find a bid. It's not going to be much fun for your partner to play in a 2-2 fit when he is looking at a zero-point dummy.
In general if you have at least 7 points or more, the bidding will go rather normally. Bid the way you have always responded to a minor suit opening by naming a biddable major. What we need to discuss, though, are those very weak hands that are short in diamonds.
Consider this hand... (And hope you never see it at the table)
Three Card Heart Suit
At first glance, after learning that you should not pass with this garbage, you probably are thinking, "Okay, I guess I will bid 1" Nope. Don't even consider it! Your response is 1 which your partner will alert and then tell the opponents that you might have a 3-card heart suit.
If your partner has a 4-card spade suit he will bid it and you can pass with a sigh of relief. Hey, you are only at the one level. The worst that will happen is that he might raise you to two hearts, but the 4-3 fit in hearts will probably be a better contract than diamonds. Another thing... you should not play support doubles for hearts, but it's okay for spades.
One Notrump Response
And if the hand above did not have that 4-card spade suit you should not consider bidding 1NT, either. Weak hands are better played in a suit. Make the agreement with your partner that a 1NT response to his opening bid of 1 shows 9-11 HCP.
Responder's Jump Shift
Most players today play that a Jump Shift by responder is a weak bid, but many expert level players are giving up on this treatment and many are now using Soloway Jump Shifts showing a hand with at least 16 points. Unfortunately, we don't get that sort of hand very often. We do however, get 6-card suits with 8-10 points frequently.
Responder's Double Jump Shift in a Major
A double jump in either major shows 5-5 in both majors - 3 is only invitational while the jump to 3 is forcing to game.