... To Doc's suggestion, but before you go to the field...
Get an empty reel (spool, whatever) the same as the one with your flying lines on it.
Set the model on its back on something soft (so's not to scuff the finish).
Put your reel (spool, whatever) halfway out from the fuselage on the inboard wing panel. Without handle but with any line clips... the wing rocks down, right?
Put the empty (whatever) the same distance out on the outboard wing. With the same number and type of line clips.
Add tipweight until the model about balances - i.e., neither wing panel is detectably heavier...
What this, and Doc's method, does is put half the line weight on the inboard tip. Full line weight at half distance is the same as half the weight at full distance. We end up with an imitation of the weights in flight, where we support half the line weight, and the model supports the other half at the leadout guides. (Not technically correct at higher line angles, but a good starting point.)
This is usually only a starting point, but a decent one. Each model is different, and many may need a bit further tweaking as you get used to flying it.