Well training stand like you train sit is differently than getting him to stand on the groomer's table. Loki would rather sit or lie down while i brush and blow dry him so I use a tip from the groomer and I put two "nooses" around him - one on his neck and one around his belly. (Yes I have a grooming table - what? It was cheap...
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To train a "stand" you ask your dog to sit, then hold your hand out in front of him with a piece of food. The second he stands say "stand" and then give him the treat. We worked on this last night in class. If you need more tips let me know, because I can explain it better but if you try that you'll start to get the idea...
For a dog who lacks confidence (and mine does for sure) you should start doing positive training. We took a bunch of classes and just started another. We did basic obedience and CGC (Canine Good Citizen) with our positive reinforcement trainer. This helps you bond with your dog and helps them look to you for guidance and since they are encouraged to do things well, it helps them build their confidence. Loki also goes to daycare with other "approved" kind, gentle dogs so he can learn that playing with big dogs is not scary. Someone is home with him all day - so this truly is a training not a babysitting thing for him. Last night at class (same facility as daycare) it only took him a few minutes to figure out the other dogs were not going to eat him and that he was safe. He really had fun working on leash with the different tricks and stuff. The BEST part was when the other dogs startled him and while he would normally *lunge* for them and bark - I have learned to read his body language and as soon as he started to I called his name and he looked RIGHT AT ME and SAT! And I shoved a big piece of chicken in his mouth. Chicken is becoming more interesting than big *scary* dogs! (These other dogs were in advanced obedience, not a single scary one there, but he didn't know that.)
Anyway, sorry for the long story but these classes don't really turn him into an obedience champion, but they do help us learn to communicate in a "scary" environment and it teaches him to look to me rather than be afraid of the other dogs. I don't know what I would do without our trainer. I'd have a monster, that's for sure.
In your case specifically, I wouldn't reach or grab for him. Instead I would hold your hand out with a treat and ask him to sit. Then I would gently pet him. Loki gets skittish when you just go to grab him - so I ask him to sit and then say "Can I pet you?" I know that sounds stupid but I'm not asking him for permission, I'm just warning him that I'm not going to pick him up. Then he sits politely. If he has been hit you don't want to use force in any way because he may think that he needs to use force back (as in, bite) If he growls BACK OFF as that is a good warning indicator and you want that. You can work on why he is growling later. Even if he wasn't hit, he still needs to learn to trust you, and he will!