As mentioned www.bricklink.com is your best friend in finding out the average selling price for your sets as well as getting an idea of what they are worth.
Remember, something is only worth as much as someone else is willing to pay for it.
This is important to note, because most of us have sentimental value attached to or LEGO's, I for one would not sell my BSB for a grand simply because to me it's worth more than money.
With that said, instructions are a must for really old sets, some people will want the box others may not, be sure you are clear what is included when listing it.
My personal preference is to do your research, decide on the dollar amount you want and then post a for sale thread on Eurobricks. Give your community first dibs, if no one bites, move onto bricklink or ebay if you choose. You may need a few more posts before you can post in the Buy, sell, trade forum.
BTW, welcome to Eurobricks as well as Classic-Pirates.com