Build from the hat down, doing arms when possible and
attaching before finishing body. Close at the bottom, gluing the feet on 
at the end.

Hat does not need to be glued, it rests on head regularly (supported 
by hair). The backpack straps and pokeball also do not need
to be glued, but in order to do that magnets are needed.
In my case, I put magnets at the bottom of the straps, between
the optional backside ((87), (89) and normal front parts (86, 88).
I also put a magnet in the right hand (25-31), and a paperclip
inside of the pokeball so they can be switched out with 
the included optionals ones. Same was done with the VS Seeker (which is why it is
absent from the picture, it fell off); a small paperclip was put inside
the VS Seeker, and a magnet between the straps where it attaches.
Parts can be glued normally as well, but magnets add the option of swapping.

It needs a slight counter weight, 
but I was able to put it in the right pocket of the backpack, since
the pockets open. This was also with magnets in the hand, so
if magnets are not used it may stand. 