Raw meat with bones (chicken, beef, pork, fish, quail, turkey, rabbit), no veggies/fruit (only as treats), omega-3 (really hard to find grass-fed meat), golden paste, lil bit of garlic, toasted pumpkin seeds. That's the usual stuff.
I changed him to raw a little less than two months after I got him. He was still really young, so no big changes from before (except pee and poop, that don't smell at all now, were disgusting before), but for a dachshund, he's really strong, fit and full of energy. The difference between him and other dachshunds on the dog park is very noticeable.