1st, avoid 6 month leases. 12-18 are the way to go. This game only makes sense if vacancies a rare.
2nd, newer tenants without an established good payment history get no breaks, for any reason (even if they are nice). You are running a business, treat it as such. I pretend that I am just an employee ( I report to 'retired me' in 10 years) and I make decisions as if this is my salaried job and I'm going to be in trouble with the boss if I manage it poorly.
It was mentioned earlier, but immediately start the eviction process with a 'notice to vacate letter'. Keep a written record of each step, meanwhile verbally let the tenant know you hope they stay as it's in your best interest too (it's true!) and all this goes away as soon as you get your rent.
I prefer not to have pets, but add into all my leases for tenants with pets, they must professionally steam clean and de-flea the house upon move out. I specifically state they must provide me with a receipt for the services or I will charge them. I also add to all my leases, a professional maid must be hired at move out and receipt provided.
So far as what you can charge, be fair and reasonable. Err in their favor. Touch-up paint would be expected, but a fist size hole in the wall would not. I few darker spots in the carpet is expected, but certainly not urine or a wine or ink stain.
Good luck. Fail fast and move on!