As a tenant, you have certain obligations to the premises in terms of upkeep and maintenance under Colorado Landlord Tenant Statutes. These obligations may not appear in your lease agreement, but you are no less responsible for not only knowing them, but upholding your obligations.
Every lease agreement carries with it an implied warranty of habitability. That is, the landlord warrants to the tenant that the premises leased to the tenant for the purpose of habitation is in fact suitable for human habitation. This does not need to be written in your lease in order to be in effect; the implied warranty of habitability is implied in every lease agreement.
Landlords who perform their own evictions may run into more problems than they anticipate regarding a notice of eviction. Colorado laws regarding the written demand for possession are strict, and must be strictly complied with or the eviction case may be dismissed.