(Full Disclosure: Mostly I just watch Gyle, then try to replicate strategies from the pros and the unmodded AI steamrolls me. Big gap between what I know to do and knowing how to do it.)
Common Strategies and Mistakes:
Pros are more likely to:
* play every faction
* gl hf
* know the meta for the map
* use different starting build orders
* get the ACU in combat
* upgrade the ACU
* reclaim
* raid mexes
* achieve air superiority
* build static D before threats arrive (e.g. AA, TML, SMD)
* use experimentals carefully
* dodge snipe attempts
* support the team (e.g. build air as air player, telemaser after losing base)
* gg
* ctrl-k their com (AKA concede defeat)
* continue to support the team even after death (e.g. ping experimentals and defenses)
* have a sense of humor
* say they are playing to win but have fun instead
N00bs are more likely to:
* play mods (e.g. phantom, murder party)
* talk smack to opponents
* turtle
* spam t1 for too long (e.g. 22 jesters)
* think every faction's t2 fighter/bomber is a swiftwind ;p
* fixate on building experimentals
* charge all experimentals straight up the middle (rarely with t3/mobile AA support)
* think the fatboy is the GC's shorter cousin ;p
* paralyse and don't build enough in the late game (t3, t4) (I think there is such a thing as "SupCom fatigue")
* beg for engineers of other factions (if you don't like your faction, why did you pick it?)
* blame teammates for their losses
* drag the game out by hiding their com in a corner
* complain about their loss even after death (e.g. offended by flanking attacks, says sniping is cheap, blame teammates)
* say they are playing for fun but rage instead
(Hope you find this helpful!)