The following regulations apply especially to landlord-tenant issues:
§ 5 states that lack of clarity is attributed to the individual applying the terms. This means, clauses that are not understandably by itself or in connection with other clauses inside the contract have to be interpreted in such a way that the interpretation that serves the best interest of the tenant applies.
In some cases the interpretation that the clause does not come into force is in the best interest. The result is that the clause in question will not come in force.
§ 9 states that an inappropriate discrimination of the tenant does not come into force. Many verdicts in dies field of law deal with this exact question. A general rule for § 9 can not be formulated, the clause is too broad. Every individual case must be examined and judged. Legal decisions however form a pathway for following decisions to follow.
§ 4 stated that individual agreements rank higher. If your contract shows additional clauses that only apply to your contract (often added in hand-writing) which state something different that the printed clauses, those individual clauses apply even if the standard clauses are in contradiction.