They do lots of things for it in therapy! Here's the ones we do regularly in addition to trying to make sounds:

Chewy Tube: This helps him build his mouth/jaw muscles. We are supposed to try and get him to chew a minimum number 20 times per side per day. Not so successful at getting him to do it when we want, but he will chew it on his own. http://chewytubes.com/

Flute: We have a recorder/flute thing that encourages him to put his lips together (he can't really do this well). It doesn't make noise unless he has his lips together when he blows.

Blowing Bubbles: We do it at night in the bath. He loves bubbles so this is the easiest! He's not good at it though - sometimes his exhale will accidentally blow a bubble, but he can't put his lips together to blow the air out. So it is great for him.

Flash Cards: We have flash cards we got that from our therapist that show different mouth positions (puff cheeks, purse lips, smile, frown, stick out tongue, move tongue side to side, etc). OH, Bun and I will pick a card and all do what the picture says. We do this at dinner because he is usually in a good enough mood to copy us. The cards are definitely hit or miss though - he's not always willing to do it and if he is, it's not for long.

I also try and get him to do things like blow raspberries and blow kisses, but he can't do these yet. I have to pick and choose times when we work on something because he isn't the most compliant toddler for this kind of thing But I try and make it short and into a game so he's interested for at least a few min!

But all these have definitely helped him! He still can't say most consonants, but is getting better with sounds. And I notice his mouth isn't open quite as much as it was - it used to just kind of hang open all the time, but now he moves it around more.

Hope that helps

we have a sophie giraffe teether. and we used to have the rubber wii remote cover that we would let him chew on. i should try the flute thing. my mom got him a toy instrument set for christmas that has a little recorder/flute. he knows you can blow into it. but he would always want someone else to do it for him.
and he loves bubbles! those are always the go-to item when he's melting down at playgroup. i've tried showing him to blow bubbles. and blowing on hot food. he just looks at me and watches me he doesn't try to copy me. i could ask his OT or ST if they have cards like that (or if they know where to buy them)