What I tend to look for are the main ingredients of instability, rich low level moisture, heat and some forcing mechanism on these models. Added to these ingredients are the winds in the various levels of the atmosphere which are part of the current models. These winds determine where the storm will go often referred to as the steering winds. The winds aloft can also act to produce vorticity such that storms could rotate in certain conditions.
Apart from the models and its associated variables, I also take into account the history of different areas of where I chase and how they can add variations the models handle poorly. Another factor to be taken into account is the available road network. It is not only useless chasing a storm you require binnoculars to see – it is also frustrating.
Models are I guess a rule of thumb approach to forecasting. Storm chasers in general use other techniques such as reading the meteoroligcal soundings for particular regions to get some concept on how deep the moisture may be, any capping that may exist, calculation of variables such as CAPE (Convective Available Potential Energy), and stability indexes such as the surface lifted Index. In Australia, the surface lifted index without doubt made long distance chasing very possible, reliable and cost effective.
Sometimes, I feel that chasers look to deeply into forecasts when really not necessary or "look for" favourable variables that suites their likeness. This can be catastrophic on some days when models or soundings may not totally agree with each other. Looking at too much information and not being realistic can make things confusing and introuce subtle errors that could prove costly in the long run.