The best way to sell is just to hold your domains and wait to be approached. That's the way you will get the best prices. While you are waiting, you should be sure to list your domains at Sedo and Afternic. It's pretty straightforward to do this - you just need to create an account (although for Afternic there is a fee). Also, be sure to have a contact form on your domains (many parking companies include this option on their parking pages).
If you don't want to wait, then you'll need to be a bit more proactive. Listing a name for sale on the various domain forums is probably the quickest way to sell. If you are not sure of the value, you can ask for appraisals first. Or, you can sell them on the forums in an auction format.
Snapnames also has a Sellers Program that will allow you to list a domain for auction. You can sign up for that here:
https://www.snapnames.com/sellerProgramOverview.jsp
Another alternative is a Sedo auction. Sedo will only let you start an auction if you have an offer on the domain (minimum offer $60). If your domain is worth more than $60, you can always get a friend to place a $60 offer so that you can start an auction. Or, you could list your domain on a site like this:
PushToAuction.com
If your domains are more valuable, I'd wait until a major domain conference and see if you can get the domain accepted into the auction there. As well, GreatDomains.com offers monthly auctions for premium domains, and you may want to submit your domain there.
The best way to start is likely taking offers in a forum. That way you can gauge what sort of interest there is in your domains without committing to selling at any price. Based on the amount of interest, you can decide what to do - perhaps set a fixed price, or negotiate with someone who has expressed interest in your domain, or send it off to auction.