Always ask yourself "can this fight bring us any value*". IF yes - fight, if no - leave. BAM now you know how to play HOTS ;-)
value: guaranteed kill without any friendly deaths, baited ults before objective, big AOE damage on most of the enemy team forcing them B just before objective, Boss kill or steal without wiping there, taking camps in right time* etc.
** right time: just before objective, to create structure killing waves if they have poor wave clear, to force enemy team splits
Hots is very simple game mechanically with rather low skill ceiling
RE: HotS Noobs, Learn To Play - Epic Channel Trailer