I'm still relatively new, and I'm having a hard time with game planning.

For the offensive plays, is it generally better too use plays that the team knows well even though the opposing teams defense will know the play as well? Or would it be better to choose plays that the team isn't very familiar with but other teams wouldn't be as well prepared for them?

I've been experimenting with it. It seems like the plays lower in the playbook either produce huge yardage or negative. Then you have some plays the team is familiar with but don't produce well.

Any other advice is appreciated!

Experimenting is the way to go. Your playbook should be fluid. Every season (and sometimes in season if I'm in the mood) I'll switch out plays with a fairly large sample size that aren't generating enough average yards and select new plays based on my players (e.g. I'll try to pick many 3WR sets if I have 3 strong WR). You should definitely always have a few plays that your team is fairly familiar with though. Eventually you'll find a balance that works.

Sounds like a plan. Thanks!