You shouldn't rent without a lease. A lease is the contract between you and a landlord (or management company), spelling out the financial and other conditions governing your time living in the landlord's property. Laws regarding enforcement of leases and tenants/landlord's rights vary by state, and it's worth contacting your state or local tenants' advocacy organization for general information about red flags to look for in local leases and legally enforceable language common in most leases.
Generally speaking, regardless of where you live, a lease will include the following features and elements:
Signature by both parties - Both you (and any roommates or cosigners) and the landlord or management company need to sign the lease and you should receive a copy of the lease to keep for your files.
Details about the property and who is occupying it - The lease should name the property you're renting and who, specifically, is living there.
Details about the length of the lease - Leases are generally for twelve months, with a specific beginning and end date. However, some leases in resort, seasonal, or university communities may have three-month and nine-month terms. Other leases may be open-ended, meaning you rent month-to-month and can end the lease with about a month's notice.
Quiet hours - Some landlords include in the lease rules regarding "quiet hours," when common areas are available, garbage collection protocols, smoke detection, utility usage, guests, pets, parking, and the like. It's worth reading these rules carefully, as the landlord can use your breaking of these rules as grounds for eviction.
Details about security deposit - The lease will include information about the amount of security deposit required, whether it will be stored in an interest-bearing account or not, whether the tenant will receive interest accrued from the deposit during their residency, and how long it will take to get the deposit back once they end their lease.
Rent payment terms - The lease will spell out the cost of rent, where and how rent is to be paid, and any late fees or penalties the landlord will charge if the rent isn't paid on time. If the landlord is offering any kind of rental concessions (rent for a year and get one month free), these should be identified or factored into rent payment terms on the lease.
Utilities cost - The lease will spell out which utilities (electricity, water, heating, air conditioning, sewage) are included with the rental unit and which utilities are to be paid for by the tenant, in his or her name.
Rent acceleration - In some markets, if a tenant fails to pay rent or doesn't follow other lease terms, the landlord can demand the balance of all rent due for the time period covered by the lease. This is considered a landlord's last resort, however, and doesn't happen often.
Right of entry - The lease should spell out under what conditions a landlord can enter the rental unit. This is necessary so that the landlord or crew can address emergencies, schedule routine maintenance issues, or show the apartment to future tenants in the event you've given notice of plans to vacate the unit. Generally the lease will spell out what times of day the landlord would enter.
Lease renewal terms - Most leases discuss the opportunity to renew at the end of the current lease term, and they may indicate by what date you need to notify a landlord of plans to renew versus move on. Many leases renew for the same time period (say, 12 months) as the initial lease, but some landlords will let a tenant go "month to month" after 12 months. Sometimes, lease renewal terms will favor the tenant picking one type of lease versus another (i.e., a rent increase if they choose month-to-month, a lesser or no increase for a new one-year lease.)