Ultimately, the best way to know what has to be repaired is to have a pre-sale home inspection done before you put your property on the market. This gives you a chance to take care of any health and safety issues in advance, rather than have a buyer walk away from the deal later.
A home inspector will provide a written report on the condition of your electrical systems, heating and air conditioning, roof, attic, floors, windows, doors, foundation, basement and structure.
If major repairs are neglected, it gives the buyer an edge to negotiate a lower price on your home. A serious buyer is going to order their own home inspection anyway. So, any major problems will come out eventually.
If you need a home inspector, a great resource is The American Society of Home Inspectors (ASHI) or call Everhome for a referral.