I keep dying~

You have to learn how much damage each weapon does and do as much damage as possible each turn. Shotgun is the only unlimited weapon that can do 50 damage, so learn how to use it. Remember which worm is going next. Sometimes it's best to put your worm next to an AI worm, so if another AI attacks you, they will at least hurt an AI worm aswell. Don't waste dynamite on 1 worm at the start, wait until there is a group/pile of worms or save it until there is only 1 worm left with less than 65 health.