Proportions and balance effect how a fly moves throught the air and how it lands.

If you wings are too long, or tied too far forward the fly tends to flip on it's head. If the tails don't extend the proper length and width the fly might sink to low. Un-even hackles or stray hackle fibers can cause a fly to land lopsided or to roll on it's side.

If you are unsure of proper proportions there are many fine tying references. Most tyers like to measure parts with respect to the hook dimensons. Purchase some well tied flies as reference guides to your favorite patterns.

For example a catskills style dry fly would typically measure the tails as 1 1/2" X the hook shank, the wings the length of the shank, hackles 1 1/2 X the hook gap, etc. While there are personal and regional differences most flies tied to these proportions will land up right.

I like to drop my flies on the tying table, if they don't bounce upright or consistantly tlt to one side I know I need to tweak them. I fly that lands funny at home is unlikely to work better on the water. Look for stray fibers that might be throwing things off, check the wing locations and ajust the size with some careful snips.