Go through your power company to see if they offer incentives for purchase and installation. Also research the company they are contracted out to to perform such upgrades if they do not do them themselves. If you seek to get them installed by a private vendor do your due diligence. I would also suggest reading up on how your company responds to solar in terms of payment for surplus energy or if they offer credits/reimbursements for a private installation.

Another big thing is the physical orientation of your house and it's surroundings, but a good vendor will do an assessment of your property before they let you purchase the panels anyway to ensure that they won't be a waste.