Normally, rent consists of the net rent and additional costs (Nebenkosten) (e.g. heating, warm water, etc.). Additional costs may be charged only if they are listed in the rental contract. In general, rent must be paid monthly in advance. Landlords may raise rent only if justified. The raise must be announced in due time with an official form. If the raise does not appear justified, you can contact the canton's arbitration authority (Schlichtungsbehörde) within 30 days.
Landlords may request a security deposit (Kaution) equal to a maximum of 3 months rent in addition to the rent. The security deposit is returned when you move out. As a tenant, it is possible in certain situations to request a rent reduction (Mietzinssenkung) from the landlord by registered letter. This is the case, for example, if the basis for calculating the rent has changed significantly.