There's a lot that can be covered here, and easy to drown in all the information online. Therefore, the following topics include direct links to try to simplify this process:
Basic definitions of landlord, tenant, and their relationship as such.
Things to look for and inspect while doing your apartment search.
Unless the place you want to rent is a shared space in a house with the owner, there are non-discrimination laws in place that protect you if you feel you're being unjustly excluded from a rental opportunity. Specifically in San Diego, the Fair Housing Council will provide you with further information.
Did you know a rental agreement doesn't need to be in writing if it's for less than 1 year? There are a number of things you'd benefit from knowing before you sign your name on a lease.
Who pays for the utilities and who takes care of the yard, if there is one? Iron out all the details in the lease so you know what to expect, and what not to expect.
Is the landlord trying to raise your rent and you don't think it's allowed? This and other questions might arise once you move in, so be in-the-know.
Who makes repairs and at what point would a unit be considered uninhabitable? In addition to the other link in this sentence, this one offers additional remedies.
When there's a desire to move out of the apartment, there may be reasons other than the end of the term without intention to extend it.
Often times the landlord keeps some of the security deposit to pay for minor repairs. Other times there are large repairs that need to be made, or too much of the deposit is not returned. Be ready for what happens with your deposit after you leave.
There are several reasons a lease termination may occur, and the steps are well-defined.
If you start getting into the area of evictions and the law, you'll need to start doing some research beyond what this site offers. Consider talking to a legal professional, especially if you want to know your legal right to retaliate wrongful eviction.
For any other legal matters not included above, the California Department of Consumer Affairs website can be a starting point.
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For information about Rental Assistance programs, consult the US Department of Housing and Urban Development website.