Attempting to apply DotA strats to real life advice...
You're not a tank so you shouldn't provoke him to start massive attacking you for heavy Damage Per Second
You seem like the the Slayer hero. She is a very good spell spammer for a quick burst of damage, but low health and being restrained by a quick draining mana pool can leave you out for a quick and painful death. Main purpose is a support damage output. You can stun and clear out the lesser enemies with relative ease while a friend with strong Damage Per Second takes out the main target. Good with the right support, but flops like a fish when trying to 1v1. Your ultimate move can deal critical damage, but it takes a long time to be able to use it so don't waste it when it won't kill him.
The main target appears to be a heavy Damage Per Second person. He can deal a continuous stream of nonsense that can pile up damage in a bad way. Best way to deal with them is to gank him. Disable swiftly and pound away. Once he is down, focus on the rest of his tea. Try to avoid 1v1 against him unless you're a tank.
This will conclude my cheesy attempt at trying to comfort you. I was never good at doing that.