((HUGS)) I know EXACTLY what you are going through.
I use these five steps (modified if need be).
1. State request
2. Restate request with reason
3. Offer help
4. Help
5. Bear Hug
I'll explain with a scenario:
Mom: Son, please pick up your shoes
Son continues playing
Mom: Son, your shoes need to be picked up so I can vacuum
Son continues playing
Mom: Do you need help picking up your shoes?
Son: NO!
Mom: I'm going to take your hand, and help you pick up the shoes.
Mom takes Son's hand, picks up the shoes and carries them to where the need to go.
*Now, if the Son is like my ds, he'll throw a holy heck fit. If that happens, we go onto step 5, the Bear Hug
It is not meant to be a wrestling move or a restraint, rather a comforting move. Does that make sense? However, if your child is like mine, they HATE being touched when they are upset. So, in that case, I'd offer an alternative that I know works. Or, I'd just remove ds and put him in a quiet area with a movie, books, puzzles, something.
Earlier today, ds had a fit. Ds is tired. He's been getting up at 6am, so by 3 pm, he's had it. BUT, he won't take a nap because he's 4.

So, when he threw his fit about the scissors not cutting the paper correctly, I gently took the scissors, put them up. Then I picked ds up and carried him to his room. Layed him on his bed. Mind you, he is screaming, crying, kicking, the whole nine yards. But, instead of reacting to his fit and giving him the energy and attention he is looking for, I turned on a movie and gently walked out. I made sure my body was calm and serene when dealing with ds.
Then I proceeded to the couch where I kicked it and punched a pillow.
I have a hard time too when it comes to fits. I keep it together until I am out of sight, then I have to release my pent up frustration. Does that make sense?