It will happen at some point if you care about the work you are doing. You will be in the midst of the rehearsal process, and realize that something between you and another actor during a scene is just not working.
You do not dislike the actor, and indeed think they otherwise do fine work. But there is just that one exchange, that one response, that one pause that throws you during scene 4 that you wish wholeheartedly did not have to occur?
What do you do?
Unless you know the actor personally, approaching them presents some risks. There are those, (I have met them)who literally will refuse to discuss any nuance or moment of their performance with any other human but the director. On the other side of that same coin, there are directors who insist that actors must never discuss a scene without they, the director being present.
Both such hard lines are wrong, and take the joy and creativity out of being in a community production. I won't be talking about such extreme viewpoints here.
But the problem remains, what does one do in such circumstances, assuming they are dealing with reasonable people?
Despitedealing with reasonable people, there is a wrong way to handle it;you should never simply tell them to change something.
"I'm having real trouble with the line pick up here. Could you just say the line with more anger,quieter,louder...etc."
Worse yet are those who would presume to actually deliver the line to the other actor in the way the have envisioned it.
In either case, bad form. Bad form because it is taking away control of the character from the actor who is portraying said character. As I have oft said on this blog, this should be avoided at all costs. (Spoken like a true actor, right?)
Instead of making a specific request of the other actor, ask them for an opinion. Try to first establish if they feel that the scene is awkward. If they agree with you that "something" is off, ask them what they think it is first, and hear what they have to say. They maybe thinking the same thing that you are. In which case, they may come to the same idea you had, thus saving egos from potential bruises.
If they problem they have seen is not the same as yours, still listen to them first, and as you discuss their concerns, discuss your own.
But even if the other actor has not felt any problems with the scene, do not ignore your concerns. You are part of the scene too, after all! Just be polite. Explain to them the problem you are having, and invite them o give suggestions as to what the two of you can do together to fix it. Then, though it was your concern, it becomes a team effort.
"I feel like I am having to rush my entrance during this scene, and I get a bit flustered. Did you notice that? Anything we can do to make the scene feel less rushed?"
With this approach the respect for every one's character remains intact,and no toes are stepped on. Only at this point, when all parties concerned have encountered a problem, and created a potential solution, would I go to the director. Even then it depends on the director, as some prefer to have actors work out small problems like this for themselves.
In a show, everyone is in it together. And those that cannot respond graciously to being approached in this manner are probably not offering much to the rest of the show anyway.