well it all depends. you will need variety of perches. some rope perches, natural branches (make sure theyre pesticide free and bird safe and heat treat them)... do not place perches above food and water bowls because they can poop in them if you do. also, make sure the perch is far enough away from the cage wall so they dont always brush their long tail against the cage.
the cage for a single bird should be no less than 18"x18"x24" any smaller is too small for a tiel. even with any cage size the bird should have out of cage time. Cage should not be a round cage, these are not good for birds. sandiperches, sandpaper covers, pedi perches, concrete perches, etc are NOT good for birds feet, they do not trim nails either so do not use them, they will cause infection and sores in the feet. dowel perches are not good for birds feet either and neither are plastic perches. they cause sores.
best food bowls to use are ceramic or stainless steel. plastic holds bacteria and are hard to clean, making it easy for your bird to get sick from bacteria build up.
Best litter to use is newspaper. It should be changed at least every other day, preferably every day. It is clean, not as likely to breed bacteria, and if your birds' droppings change you can tell easier. Do not use Carefresh, wood shavings, sawdust, corncob, sandpaper, etc as these are not good. These breed bacteria very quickly and cause bacterial infections in birds. Also, if a bird eats these they can choke or get an obstruction. Newspaper, brown butcher paper, paper towels, white computer paper are acceptable and safe. Newspaper should be black and white. Do not use the glossy newspaper as the ink may be harmful for your birds.
Cuttle bone is an important thing to always have available as well
they should also have toys. A lot or a little is up to what your bird likes. toy wise, make sure it is safe in general and for your individual bird.
here's how my cage is set up for two