A few ideas...
Add some herbs, or some garlic, bay leaves can help too
Add some more vegetables such as celery, onions, carrots etc
Use a sachet of proper liquid stock, instead of bouillon cubes
Add most of the flavours at the start, so the meat is cooking in the sauce (rather than cooking the meat and adding them at the end)
Also try browning the meat first, unless its a tough piece which really wont tolerate even gentle frying.
This isn't done to 'seal the juices', but to create flavour via a Maillard reaction.
-------------
I made this in my slow cooker yesterday, it was nice and tasty....
Chop up 8 pork sausages into 4cm pieces, and brown them in 2 tablespoons of olive oil
Optional: I also chopped up a 3cm cube of chorizo and sauteed that for a few minutes
Remove the sausages and set aside to drain
Now roughly chop 3 cloves of garlic, dice one large onion, and 1 large carrot
Add the vegetables to the pan with the sausage fat in it, and sautee until onion is soft
Add 2 teaspoons dried rosemary
Add 200g of cooked brown lentils, and 500ml of chicken stock and give it a good stir
Add one large whole red chilli
Bung all of it in slow cooker and cook on high for 2 hours, or low for 4-6 hours