When things are happening quickly then you may need to use automatic modes like Av and Tv, but the best advise I can give any amateur is to learn how to shoot in Manual Mode. Every other mode is automatic to some extent.
If you use Av or Tv then your exposure is being worked out by a mathematical formula devised by some technician in Japan based on an average light reading of some sort that may have no bearing on the correct exposure for your subject. Then you have to worry about varying amounts of exposure compensation, which is just correcting for getting it wrong in the first place. That is because the brightness of the subject will be incorrectly affecting the exposure, even if the ambient light is not changing.
Once you get the hang of Manual then it soon becomes instinctive and works in very situation from wildlife to studio. Depending on whether you are Canon or Nikon or how you set it up your thumb is always aperture and your forefinger is always shutter speed. Three clicks of either wheel is one stop. Conversely, if you change between Av and Tv then you are always having to think about controls what.
