One thought...
Borisoff,
You have asked whether a person should implement the new motivation first or the new behavior first when that person is trying to acquire new behavior, such as smilling at people.
Most people want to be doing their new behavior for the right reasons. In some cases, it's worth forcing the new behavior for a while and the motivation may catch up (example: may be worth quitting the behavior of smoking and sticking to your guns even though you don't 'feel like it' partway through). In other cases, the motivation may matter more. (I can't think of a specific example).
I tend to lean toward behavior first. If I make myself smile, I already will feel a bit better (though sometimes I don't WANT to).
If you don't like people, how about smiling at them and, while you consistently do that habit, trying to learn to like them at the same time? I know it's a hypothetical, but that'd be one approach.
JohnV474