Probably the most significant factor in determining whether (homophone intended) a flight will be performed at all in general aviation is the weather outside. You may be able to ignore a mild headache and fly, but probably not a low-level wind shear warning.
For a summary and guide to some effective weather forecasting tools you can and should use, look here.
When it comes to developing a better understanding of METARs and TAFs there are some resources compiled here.