Different people probably have different methods, but here's what I do:
1. Hold plane securely in right hand
2. Hold Tx securely in left hand. Make sure all trim settings are in desired postion and the antenna is extended. Be sure to hold tx so that antenna does not hit plane!
3. Using left thumb, slide throttle to full while mainting grip on tx (easier said than done). If this tx has a throttle trim and the plane is under powered, you will probably want to slide the throttle trim all the way forward as well.
4. Launch plane as you would if throwing a ball or a dart, not too high, but with an upward angle at or less than 45 degrees.
5. Get tx in both hands and level off plane if it is still climbing, give some up elevator if plane is diving, etc.

Easier to show than tell, but I hope this helps