There are two kind of grips. One, the Lifting(Flight)-arm Grip and two, the Dingle-arm Grip. Both the grips will work provided the boomerang is held with the flat side away from you. In general, Dingle-arm Grip will produce a lower, more circular flight, better suited to windier conditions and stronger throws. In either case, the boomerang should be cocked back along your arm so that plenty of spin is given automatically on launch, and the grip should be reasonably firm to allow a clean release and control of tilt and trajectory.
Standing at a wide area or a field, feel the wind around you. Now, face the wind. If the wind is quite strong, wait for a while or your boomerang will be blown away. In other words, it will not come back to you!! Strong wind should be avoided when throwing. Like any flying device, boomerangs are greatly affected by wind and blustery condition make return flights impossible and crashes more likely. Ok, at about 40-50 degrees to the right from where you are standing, you're ready to throw!!
The thing that beginners always do is that they think that boomerangs are thrown like a frisbee, which is thrown horizontally. Well, a boomerang is not thrown that way. A boomerang is thrown almost vertically but not too vertical. Keep an angle at about 5-10 degrees when you throw. NEVER LAID OVER FLAT!
Don't ever throw like this!!.
The outward tilt of the boomerang has a great effect on the height and stability of the flight. Too much tilt will cause the boomerang to swoop and stall, giving it an unpredictable flight and making catching difficult. If you throw the boomerang laid over flat, it will climb very high, stall and then come crashing down vertically. In this event, the risk of damage to the boomerang is high, as is the danger to yourself and to bystanders, so this practice is definitely not recommended. What you need to do is aim just above your eye-sight and throw.