This is an interesting video of a training session with Max (12 months) which illustrates the importance of paying attention to the relationship between the infant and the physical environment.

Initially I help Max into standing with his feet fairly close to the foam block which provides the support surface for standing. This makes it difficult for him to balance as he still tends to stand with some hip flexion.

To stay upright and engage with toys that are quite close to the edge of the block leans back against my hand. He also starts to sway backwards and forwards to explore that is possible in this situation, which then turns into a fun game.  

Next in order to get him to stand without help from me I place the toys just beyond his reach and eventually he leans forwards with his chest against the block, which frees up one hand to reach for toys and allows him to stand without my assistance.

Towards the end of the clip I move Max's feet further back which allows him to tip his trunk forwards and lean on his forearms with his hands fee to play.