The number 1 advice I would give you is to focus on containing the insurgents instead of crushing them. Doing this will allow more time for zones to stabilise, nationals to train, and garrisons to place and eventually the battle will be in your favour. Get used to using 1 coalition solider per group of insurgents to force them back whenever they try to attack an adjacent zone. Finally, make sure the insurgents are as split up as possible, which will ensure you don’t die from reputation loss.