I have just started painting the arms separate from the body.
I used put together the whole model then paint them
But as good of a painter that you may be there will still be bare spots.
I really makes the difference painting the arms separate.
I use a cork and paperclip to make a holder to attach the arms,head and gun to.
I also use them to hold the models while painting
Next time someone polishes off a bottle of wine try to snag the cork.
They make great basing material for craggy rocks but they have an even better use.