LEAN = HOT / RICH = COOL.

Look up the factory needle settings for the engine you have and start there. Factory settings will usually allow for easy starting and are slightly rich. This will give you a good starting point.

Make sure you are using the correct glow plug for your engine also. Don't cheap out on glow plugs, always buy quaility plugs as they are very important.

Any other info you can provide will only help you get the info you need.

Type of fuel: Brand & Nitro %
Glow plug: brand or #
Always make sure there is a trail of blue smoke coming out of the exhaust under acceleration.
If not...richen it up.