Hi LuckyBird
Welcome. Can I recommend a tiel care guide if you havent got one yet? And be careful what you read on Google/Bing. I'm new to cockatiels too... trying to learn as much as i can because parrots are complex. A few tips off the top of my head:
~ as Sunnysmom said, need to add pellets and veg (particular kinds and some only occasionally such as those with high oxalic acid) as seeds are too high in fat (can cause fatty liver) and lack essential nutrients
~ some shredding and foraging toys, and maybe some training for your tiel in how to benefit from them
~ a nightlight to help prevent night frights
~ clean water bottle and replace water daily as they quickly contaminate the water with droppings and their beaks
~ avoid drafts and a/c
~ search for suitable toys that don't present a choking or trapping hazard
~ be careful with home surface cleaners and don't cook stuff with teflon pans
~ nicotine is deadly, so careful with smoking/vaping
~ Tiels like all parrots need flight time in a secure area, and there are things to learn about stress-free/low-stress cage infils and exfils
~ Learn as much as you can about body language (head and beak movement, tail, body feathers, wing movements and so on) so you can start learning about how to read the needs of your tiel before he/she feels frustrated with communication difficulties and starts exhibiting more drastic behaviours
~ training your tiel helps you both to form a relationship, facilitates such tasks as cage entry/exits and provides stimulation for your bird. Try to locate a primer
~ Use positive reinforcement rather than negative and see what Pamela Clarke said about antecedents
Maybe you know some of this or some of it doesnt apply. I also recommend you read Pamela Clarke's advice on avoiding pair bonding. She also gives suggestions on simple toys. I imagine others with much more experience than I can add to my list (and maybe modify it).
How old is your new tiel? M or F? Feel free to share some pics!