How do I engage in a teamfight as an ADC?

Hello everyone. I'm creating a post in order to satisfy the trouble I'm having when engaging as an ADC in a fight. Take for example, I play a game as Kog'Maw. I have 3 items, and am prepared to demolish the enemy frontline and force the team to retreat. The next action I take before engaging is to stand far away back, activate W, and than start firing. However, this often doesn't work in my favor as my frontline get's CC'ed into obilivion and than expose to me to the assassins who one-shot me. Now, that's obviously just one scenario, and I know there's many more. I just want tips on how to engage and position my self correctly(Dragon, baron, full 5v5, ect). Note: I'm lvl 28, so the terms I use and the things I'm asking for may be totally incompetent or be not necessary due to my lack of LoL experience.
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