Hey purpletree.

One thing i noticed is that you're looking to add more stuff, rather than trying to work on the things you already have in the piece. I don't have much time to give you any great advice but i'd suggest trying to imply your forms using shades rather than lines. The flag is outlined but the golfball isn't, which is strange because the flag is presumably made of cloth or perhaps thin plastic, yet the ball is solid and heavy, so really it needs more  presence given to it than the flag. At the moment it is lost in the light green floor.

Give the ball a shadow and some more form, don't be afraid to exaggerate it's size to add that extra bit of detail (although in doing that you'll have to work on adding a stylistic theme to the whole piece, so you'll have to think about that when chosing to do it). Think about the walls, the two planes aren't really separated at the corner like it seems with the black line. Think about the flag-pole - is it black? Is it a void? It seems as wide as the outline to the flag... should that really be what you're trying to convey?

Heh, wrote more than i meant to. Anyway take from that what you will.

here's a little update,