The accompanist's job is to make the soloist look good. They're right, even when they're wrong.
Learn your part. Learn their part. Then be able to play your part and sing/hum their part.
Ask or watch how they will cue you in, if that's an issue at the beginning.
Ask how they want to you provide a tuning note. Some want just a note. Others want a chord with it or more notes.
Make sure you learn your part. It depends on the situation for accompanying. Some things -- school, church, less important performances -- you don't have to play it as written. Others you do. If the soloist doesn't know what they're doing, you can take more liberties, but they probably expect you to play what's written.
But sometimes the soloist doesn't know how to cue and things like that. A head nod, a breath in time. Nonverbals like that give you the info you need.
Make sure you can see them during the performance.

Duh, yes, but still important. And if the soloist doesn't understand that, then make sure they know.
Some accompaniment is background. Other pieces are more like a duet. Don't be afraid to play out when it's your turn in that case.
Sounds like playing in an ensemble may be an issue. Tap your foot. Nod your head. Be able to show the beat like that. Not that you will use it, but you might want to have that for rehearsal.
You also tape record. Tape the solo yourself, then practice with that. Tape yourself taping out the beat as you follow the score and practice with that.
Flutes might want a Bb or F to tune to.
If you're not secure with it, ask for more rehearsals. You can get the tempo issues down more then.
And it's not the most important thing in your life. It may be for the soloist, but not for you. Just be aware of where it fits into your priorities. If you're doing solo stuff too, don't let that suffer. It's always a balancing act though.
It's also possible just to play your part, with a steady beat, and let the soloist fit into that. If the piece generally has a steady beat throughout, it's not that big of a deal to sync things up.
Work out the pay ahead of time. And the schedule. When is the performance? How many rehearsals, where, and when? What do you wear? Do they get a page turner or do you? Make sure the page turner can read music.
The beat is the most important thing though. After practicing with them a few times, you'll figure it out. If it's a concern, just try to meet sooner rather than later.
Ah. I see it's this week. Just meet and work things out. Do whatever you need to do. For some "less important" music I just sit down and read through it and "fix" whatever the first time around. By fix, I mean simplify or rearrange. So that the second time I play through it, it goes smoothly, no problems. Usually, that's simplifying things to a certain level. That way I start engraining it the second time I look at it. If I make it easy enough, I have plenty of attention left over to pay attention to other things, like the soloist.
Practicing starting the piece a few times. Practice the transitions and rit's, etc. Anything were you have to communicate. You don't have to run through the whole piece very much. Maybe twice in a rehearsal. If that.
Once things are solid, make sure you're playing the same style. Copy the soloist phrasing, articulation, etc., so things are more consistant throughout.
For beat concerns, just make sure you can see the soloist out of the corner of your eye. If you're off, they should be cuing you a little. They should be helping you out too. They can do things that make your job a lot easier or a lot more difficult.
And when the performance is done, compliment them and tell them you enjoyed doing it and they played well, etc. Even if they didn't. It's just professional.
And you make sure you're learning something the whole time. Regardless of the performer's level, there is always something new you can pick up from them.