There is nothing better than experience to help you out on this.
Don't get too hung up on what the professional game does, there are differences in expectations (and skill) at the professional level compared to what happens at grassroots level.
The best advice I can give you is to go with your gut feeling on what you judge to be a caution/sending off, and try to gauge how it will affect your overall control - you will get things wrong, don't worry about that, that's part of the learning process. There's generally a happy balance between punishment and control of the game. As already said, go with your own judgement but be prepared to revise that judgement over time.
If you can, attend training seminars by your area assoc or the referee's society, they will usually cover fouls and misconduct and the punishment you should go for at the various levels, usually in video form which will help massively. If you happen to get assessed pay particular mind to what they say about your handling of cautions and dismissals, their advice is often excellent.