The main one is to give them lots of toys. Take the perches out of the cage and replace them with twigs and branches you cut from your yard, or from somewhere you know doesn't spray.
They don't have to go straight across. They can cut a corner or be at an angle. Use a couple of pipe cleaners to make a short, thick one into a swing. Budgies love stuff they can shred, bark they can chew and bells they can ring.
You can actually just have one perch, one swing and a bunch of toys. They'll likely sleep on the swing and they're happier having lots of things to do than lots of places to sit.
When I do new branches, I do one thicker than my thumb, which becomes a favorite for chewing and sleeping on, and one thinner than a pencil, which becomes a trampoline and has to be put back up every other day. My birds favorite toy is when one chewed on the swing branch till she actually chewed through it and it was just a twig hanging from one side. They LOVE it. They climb up and down it, spin on it, make a game out of catching it and working at it until it's draped over another perch. So much so, that instead of fixing it, I just replace it with something fresh and leafy once in a while.
The rope coil perch was another good one. They didn't touch it for 2 months and then were all over it until it needs replaced (Neon has a very busy beak). But, a warning, if you do get a rope perch, keep an eye on it, clip any threads that come loose and replace it when it gets worn. You don't want any little toes caught.
They don't strictly need a cuttle bone but they love it, so I get it. Not a lot of them bathe, but the ones that do, LOVE it. I just use a great big thing for their water and they can indulge whenever they like.
