Having your dog on a long leash and guiding them into when you call them to come. Lots of praise and treats when they do come to you. If your dog is off leash and you are calling them to come, they have the option to come if they want. So you should have a reliable recall on leash before you can expect one off leash. Also, another thing I do when Molly is off leash (in an enclosed area, like our yard) and I want her to come, is I start to run in the opposite direction and that gets her to want to run after me. When she is coming, I tell her "good come" and praise when she gets to me. Repeating this and being consistent will help with a reliable recall.
Get a long clothesline and use that as a way to reel the dog in when you call.
Seriously, as a general rule you should never ask your dog to perform a command that you cannot enforce. Otherwise, they quickly learn that they don't really have to do what you say unless they feel like it. Sometimes that may be okay...but there are two commands that really need almost perfect performance: "Come" and "Drop it." Those are the two that could save your dog's life.
In addition to reeling in the dog with a long line, I'd encourage you to treat every time the dog does come to you. Make it so that the dog expects that coming to you will be far better than anything they've found in the yard--because coming to you means a piece of cheese, or whatever is a favorite. And obviously, never call a dog to you and then scold him. ("Where were you, I told you to come five times you bad dog!") That's just reminding him why he shouldn't come next time you call.
In addition to using the long line to make it happen every time you say come.. Don't ever, EVER call your dog to come if you CANNOT make it happen.. All's that does is teach the dog that he doesn't have to come.. Find some "other" word to use or walk the dog down..
I too use a long leash and pull him in if he doesn't want to comply. The recall command should be viewed as mandatory all the time. it is one of few commands I expect 100% all the time. Never issue the recall unless you can be sure he'll do it or that you can make him do it by pulling him.
When my boy comes back (on or off leash, weither I've reeled him in or not) I give treats and prasie and make a big deal. comming back to me = a big love fest and goodies.
Long leash and lots of praise and treats works, but be super consistent and never allow non compliance on recall...as others have mentioned the recall is a command that could very well save your dogs life.