Valerie,
Great question. What I want to say (because I am an attorney) is that you should always involve an attorney... but... here's my two cents.
First, you should NOT just grab a lease agreement from the interweb and hope it works for you. You should talk to other landlords, ideally someone that has been around for a while and see if they will pass their lease along. Also, some nice property managers and associations such as the Department of Real Estate or Apartment Association may have a lease template or form that will be specific to your state laws and one they use for multiple tenants. These should come for free. If you have the advantage of reviewing several and choosing one that best suits you, great. If you can't get your hands on one, getting one from a real estate attorney for a few hundred dollars is well worth it, especially since you will be able to reuse it again and again. I even know of some RE attorneys that give out a lease form to new landlords.
Once you decide to become a landlord, you should begin looking for and building a relationship with an attorney. The reasons for this are many but an attorney can advise you about your risk of liability and what you can do to avoid being sued and what you can do to limit your exposure if you do. I would say that once you become a landlord, it isn't a matter of "If" anymore but "when" you will be in a dispute with a vendor or tenant about the property and you'll be glad you have a good relationship with an attorney who knows your situation.
He will likely recommend you transfer your rental properties into an LLC, and for good reason. Many people here on BP think that an insurance policy is all you need or that an LLC isn't necessary. This however is not true. There are many reasons you should use an LLC for rental properties, and have good insurance coverage.
While attorneys don't give tax advice, they should know enough about entities and your situation to help point you in the right direction regarding taxes and connect you with a good accountant who can make sure you take advantage of all legal tax strategies to reduce your tax obligation and pay only what is required. This will save you thousands of dollars over the long term.
It should not cost you to have a consult with an attorney to tell him about your situation and your goals and see what his recommendations are. Do not wait until you are already in a lawsuit to try and plan a way out. Take the proactive approach and do those things that will reduce your risk and probability of being sued to begin with.