Its a very good idea to be thinking of hands in terms of whether they are balanced or not.
These shapes are balanced.
4333 is the most balanced shape. But also 4432 is regarded as balanced. These days 5332's are also thought to be pretty balanced.
When you are balanced, its very often a good idea to respond 1NT when you do not have a major.
Partner opens 1♣ and you have
The correct bid is 1NT. Forget about that diamond suit. 1NT nicely conveys your hand, 6-10 points, balanced. Save 1♦ for the hands where you are unbalanced.
What about this hand? Its the same idea
Confidently respond 1NT.
What about this hand?
Most of the time when partner opens 1♣ they simply have a generic balanced hand. Most likely your hand belongs in No trump, as you are balanced and likely your partner is also.
Respond 1NT, start off by letting partner know that you are balanced without a 4 card major. If that ends the bidding or if partner responds 3NT, you should feel confident about the contract. If partner has long clubs, they may bid them next. In which case it won't be too late to show that you also have club support within your balanced hand.
Partner opens 15-17 No trump, how many points do you need for an invite? (if you play different range No Trump, say 14-16, you will need 1 extra point to invite than the recommendations below).
The main point is with a normal balanced 8 points, just pass. An invite should be done on 9 points, or a very good 8 point hand. With 10 or more, bid game. Often people worried about missing game if partner has 17. I'll keep the explanation brief and just say, forget about that.
This hand is not an invite.
But that does not mean we always pass with 8, for example.
This is quite a nice hand, because it has several 10's and good quality suits, you would not be ashamed of inviting on this hand. A nice idea is to look for a major fit by bidding stayman, and then fall back on an invite.
Of course with distributional hands, its a different story, for example the below hand is only 7 points, but bidding 3NT is a fair approach, as the hand may be worth 5-6 tricks. (People often value a good 6 card suit as 3 extra points!).
Overall, the key point is that with a normal balanced 8 points, its advisable to pass a strong NT, and to invite with 9 points. Not all balanced 8's are equal, and occasionally it is a good idea to bid on, especially when you have the majors.