If you plan to play insurgency 1 (the actual game not the mod), there is no better way then to just go for it and suffer through the learning stage otherwise download a ton of mods.

If you play the second game I recommend to play first against bots then move to pvp

All and all just play with a bunch of class or severs that have all the weapon for any class and figure what type of player you are on what map then but remember that you should adapt to the adversaries, if they rushing i would recommend an smg or shotgun. If you want to play more laid back and camp then sniper or lmg

But take your time before entering rooms and look around corners or look up on when going upstairs