I just throw mine in with whatever I have in the cupboard!

Onion
carrot
Capsicum
Leek
tin of crushed tomatoes
some cherry tomatoes if I have some which need using
if no tinned tomatoes, whack in a bit of tomato paste
fresh rosemary
a bit of wine if there is some open
enough stock to cover

Are you using a dish in the oven or a slow cooker? If I'm using an oven dish I brown the onion, carrot and shanks first, then add the rest. Make sure you cover the dish with a lid or foil so the liquid doesn't evaporate and you end up with dry shanks. If I'm using the slow cooker I just throw it all in and let it go. If you want a thicker gravy, remove the lid for the last 20-30 minutes of cooking or throw in some gravox for the last 10 minutes or so.

Are your shanks frenched? If not, you may need to scoop some fat off before you serve.

I serve mine on mashed spud. Mmmmm..... shanks.