How to approach Lease Violations--Rookie First Timer Landlord

[Timothy Burns]

To clarify my situation, I am in my first year of landlording, househacking a duplex, so I live next door to tenant. 

Tenant hasn't even been here a full six months and has broken the lease I feel several ways, but Im not sure how to approach. 

1. Smoking excessively: during pre screen tenant stated that they only smoke outside, but now the bedroom smells like an ashtray and they are leaving butts all over the premises. 

2. Pets: stated clearly during pre screen that they would not have any pets becuase they didn't want the extra responsibility, but they now have a rabbit. 

I first became aware when I was working on the kitchen sink and saw a bag of rabbit food under the sink, and since then have confirmed that they do indeed have one, but they are not aware that I have seen it. 

3. Longterm guests: this one doesn't bother me as much but they have a minor that has basically been living there, not so much that I don't like them staying, but I believe she's been doing laundry over there (can't really prove that)  and I pay for water/sewer. 

I have been taking pictures of all this. 

Not sure if I should just go ahead and put a notice to comply in the mailbox or are there other steps I need to take first? 

[Nathan Gesner]

Quote from @Timothy Burns:

You should give them a written warning and a demand that they correct the violations within X days and pass an inspection. If they fail or refuse, you serve them notice of termination and expect them out in 30 days. If they fail or refuse, you evict.

There's much more to it than this, but it's hard to write a step-by-step guide for everything involved. The bottom line: if you have a rule, you need to be prepared to enforce it swiftly and professionally before it gets out of hand.

Do yourself a favor: buy "Every Landlord's Legal Guide" by NOLO. Written by attorney investors, it's full of practical advice pertaining to management of investment property, has sample forms that can be edited, and - most importantly - they tell you what your primary state laws are and where you can read them. It's updated every year and is the best $40 you'll spend as a Landlord. There is one book for 49 states and a separate book for California.