We've discussed how to decide which suit to bid first, and how many cards you need to bid. Those were specific requirements. Today, let's consider what you should be thinking after your partner opens the bidding with one in a minor suit. To make things easy, we'll say your partner opened 1 club and your right-hand opponent passed.
Let's start with your easiest decision. If you have less than 6 points (counting distribution) you should pass. It makes no difference if your partner opened 1 club and you are void in clubs. Pass. Your left-hand opponent is not likely to pass out 1 club. Even if she does, your partner might be able to squeeze seven tricks out of the hand. This call doesn't take a lot of thought.
OK, you have 6 or more points. Now, you MUST bid. Your partner's bid is not forcing, but your hand is strong enough that it demands a bid. You might be thinking, "Six points is strong?" Well, no. It isn't, but your partner has at least 13 points and could have more than 20. Your 6 plus partner's 13 gives your side about half of the strength in the deck at a minimum. You want to give your partner another chance to bid.
OK, so you have determined that you are going to bid. Now, what should you be thinking?
First, don't think too hard about supporting your partner's clubs. Partner needs 5 cards to open a major suit, but just 3 to open a minor. Minor suit contracts are worth less than major suit contracts, so give your side a chance to find a major suit fit.
With more than one 4-card suit, you are going to bid them "up the line." That is, bid the cheapest one first. If you have diamonds and spades. Bid 1 diamond. Now, you may be thinking, "Didn't you just tell me we were trying to find a major suit fit?" Yes, I did, but bidding 1 diamond won't prevent you from finding it. It gives opener room to bid her 4-card major suit (also bidding "up the line") for her rebid. The requirement for opener to have a 5-card major suit is just for the opening bid. If you partner has 4 spades and not 4 hearts, she will bid 1 spade at her next turn. You've found your spade fit. If she has 4 hearts, she will bid 1 heart at her next turn. Then, you can bid your 4-card spade suit in case she has both 4-card majors. So, you see. You still find your 4-4 major suit fit.
Suppose you ignored or forgot my advice and bid 1 spade at your first turn. If partner has 4 spades, no problem, but if she doesn't you may have caused a problem. Suppose she has a 4-card diamond suit and 5 clubs. You'll never find the diamond fit. She presumes that you don't have 4 diamonds because you skipped over them to bid spades. You are likely to end up in no trump when you might have played a comfortable diamond contract.
So, keep this in mind when responding (and rebidding as opener). Since you bid your 4-card suits "up the line," any suit that you skip over implies that you do not hold 4 cards in that suit.
Now, what about hand strength? Your new suit bid doesn't narrow your point range by much. It could be 6 points. It could be 18. That is nothing for you to worry about. Your new suit bid is forcing for one round. Either you or your partner is likely to make a bid on the next round that will narrow the point range for one of the hands.
If you have two suits of unequal length, bid the longer one first. You will still probably be able to find a fit in your 4-card suit if partner doesn't have support for your 5-card suit. Consider some examples:
Opener: 1 club
Responder: (has 5 spades and 4 hearts) 1 spade
Opener: 1 no trump (minimum opening hand, lacks 4 spades)
Responder: 2 hearts
Opener: "Aha! My partner must have 5 spades and 4 hearts. Otherwise, he would have bid the hearts first. That means I can support his hearts if I have 4, or his spades if I have 3"
Opener: 1 club
Responder: (has 5 hearts and 4 spades) 1 heart
Opener: 1 no trump (minimum opening hand, lacks 4 hearts)
Responder: "Hmm. My partner passed up the chance to bid 1 spade, so she must not have 4 of them. There is no use in my bringing them up. I'm not that crazy about being in no trump. I'll show my partner that I have 5 hearts." 2 hearts.
Opener: "Aha! My partner must have 5 hearts and probably 10-12 points. If he had 13 points, he would have jumped in hearts. I've got 3 hearts to support his 5 hearts. We don't have enough strength for game." Pass
Suppose your only 4-card suit is clubs. That isn't enough length in clubs to support partner's possible 3-card suit. Bid no trump. 1NT shows 6-9 points. 2NT shows 13-15. 3NT shows 16-18. What about 10-12? Yeah, that one is tricky. Your best bet is to "invent" a diamond suit and bid 1 diamond. Your bid is forcing for one round. Partner might rebid clubs showing 5. She might bid a 4-card major. She might support the diamonds that you don't have. With anything except a club rebid, you can bid no trump at your second turn. Your partner will figure out what you meant...maybe. You could try a limit double raise to 3 clubs, instead. You might end up in a 4-3 club "fit." Not every hand fits nicely into the structure. Sorry about that.
Finally, if you have 5-card support for partner's minor suit, and no 4-card major, you can raise the minor suit. A single raise shows 6-9 points. A double raise shows 10-12.