Even though they don't recognize something new as food....pet cockatiels notice what YOU eat and will want to taste it, but don't let them eat from your mouth. Hookbills (parrots) do not need grit to digest their feed. It is recommended that you don't give cockatiels grit. An exception is oyster shell, my understanding is that oyster shell can be digested and absorbed.
[LEARN the safe and toxic plants before your bird has access to any].

 CAGE & IT'S LOCATION:
 20"x 20" x 18 H" is the minimum size, with a large platform door, 3/4 inch bar spacing. There should be bars running horizontally for the cockatiel to climb up with. Round, tower cages are great-looking but not good cockatiel cages. It is important the cockatiel can open it's wings without hitting something or the sides of the cage. Don't cramp it by loading up the inside of the cage then with too many toys.  Cockatiels are powerful flyers and frequently need to exercise their 14+ inch wing span  by hanging onto a perch and beating their wings. Cockatiels love coming out to a playpen on the top of the cage.
Perches of different sizes are very important for the bottoms of your bird's feet, don't let them get pressure sores, (a difficult condition to heal in my experience). I love the natural manzanita branch perches. Scrape dirty perches clean. (Damp perches aren't good). Wash the removable wire cage bottoms weekly. You can use diluted bleach or apple cider vinegar or white vinegar when you wash your birdcage.
Cage LOCATION has to be in a draft free area, not near registers, fans or air conditioning, or direct hot sun light.
The kitchen is a hazardous room because of cooking steam, also overheated Teflon is a bird killer. Cockatiels are very susceptible to strong smells such as insecticides, smoke and air fresheners. Their respiratory system is so efficient some of these can kill a cockatiel.
Don't buy gravel coated perch covers or the mite protector to hang in cage. WATER containers are the most common place for bacterial buildup and should be washed daily. Water bottles are not an excuse to let the water go unchanged daily. My cockatiels take a drink when I give them cold fresh water. They like it better too! When offered the choice, birds always prefer cool bath water over warm.
Change the cage bottom paper daily. Mold spores from uneaten food and dried poops getting airborne cause respiratory disease infections and other possible disease spread in the bird's air space. (The reason that quarantine has to be in a different room.)

DAYLIGHT & DARKNESS  [from Lafeber]
Nature constructed birds live within a balance of day and night, in fact, the influence of daylight and darkness has been so great that it has been said that birds are a "slave to light". Many effects can be had by shortening and lengthening the amount that the bird receives in 24 hours.   Poultry raisers for years have stimulated increased egg production by having the lights in their poultry houses remain on extra hours after sunset.  Bird's migration is partly based on days becoming longer in the spring and shorter in the fall. Pet birds probably require the same amount of light and dark that are occurring in a natural day.  In the summer the birds would have eight hours of darkness daily and in winter they would have about 12 hours of darkness daily.  Birds in the family recreation room that are kept up until midnight every night because of the television programs and who then have their sleep cut short in the morning because the sun rises early or light is turned on may be receiving only five to six hours of sleep every day. Inadequate amounts of rest for birds will cause constant stress and eventually will show the result of this in a breakdown of their health. The periods of light and dark can be controlled in pet birds with a heavy cage cover.

 GROOMING:
 WING TRIMS Reasons for trimming wings are #1 It won't escape from an open door. #2 It helps in taming and training, by keeping it subordinate. Reason not to trim wings: Flighted birds are trim and toned if they have room to actually fly.
Have an experienced cockatiel breeder (preferably), or an avian vet show you how to trim the cockatiels wings and toenails. It doesn't hurt when you trim feathers or nails. If you accidentally cut a blood-feather (a new feather encased in a keratin sheath with a blood source at it's base), it will bleed and you just have to pull the feather (straight) out to stop the bleeding.
Make sure to look at the UNDERSIDE of the wing before making a cut! You will know a blood-feather.

The nails have a blood vein in them, if you cut too much of the nail tip have on hand cornstarch or 'kwick stop' to apply to a bleeding nail. With a little practice, you can groom wings and nails yourself.

You can take an emery board and file the tips of the nails, (very safe and effective for pet birds when their nails feel like little needles to your skin). Observe your bird's nails as the bird ages, you may see that it's nails curve making climbing in the cage difficult. Look at the bottoms of the bird's feet occasionally to see that they are in good condition.

BEAK TRIMS it is unlikely that your cockatiel will need its beak trimmed at all, if you provide a cuttle-bone for it to chew on, but if you think your bird's beak is overgrown... I strongly advise you to seek an avian veterinarian to find out why.    It may be a disease or fatty liver (diet) related.
A bird's beak has sensory capabilities and contains a blood supply. This tells the bird what he has in his beak and basically whether it is food or not. To damage or crack the beak so it will not re-grow normally would pose a threat to the bird's ability to eat. Little wonder that it is traumatic for a bird to get a beak trim.
Please do not ever try trimming your bird's beak yourself. Take it to your trusted avian vet first for an evaluation.