The most common advice is also the most correct. The more Flyrants you have, the better you'll do. Two is very literally the minimum. You will struggle with less than two against all but the most casual of players.
Tyranids are in a bad spot with the many 3+ saves and almost no Invuls, so they get hurt very badly against Plasma and Grav, but a big thing to mention is that there are no tanks, so enemy anti-tank weapons have to find a target. Because of this, avoid Warriors as best you can. They get insta-gibbed by S8+ and as I said, that S8+ usually has nothing better to do.
Deployment tricks are a must. Mawlocs, Tyrannocytes, Outflanking Tervigons from making them a Troop Choice and giving Hive Commander to a Tyrant, Lictors, these are all thing to really think about. You won't survive the walk across the table so you have to have ways to not walk. Different players have different methods outside of the pure competitive Flyrant Spam, and you'll have to find yours. If you have to walk, Venomthropes and their Forge World brother the Malanthrope need to hold your hand. Shrouded bubbles keep things alive for atleast a little longer.
Formations are powerful. Our Heavy Support slot is packed, so look at a Formation to losses it up. For instance, Living Artillary Node is a popular choice for new Nid players, and is strong enough to consider in the majority of non-tournament metas. It clears up some slots for more Mawlocs or Carnifex by taking Biovores and an Exocrine out of the place. The Elite slot is another packed one so consider Formations that use Venomthropes there to free up room for a Lictor or two, some Zoanthropes and so on.
Commit to a playstyle. Middle of the road average is just death to Nids. If you swarm, swarm it all. Take enough Synapse, but avoid big bugs other than Flyrants and Tervigons. If you do Nidzilla, do not take a single Gaunt of any type. If you want the skies, don't take anything that moves 6" other than a Malanthrope to give Turn 1 protection before your bugs take flight. Go all in on what you want to do and make sure you have PLENTY of Synapse at all times. Flyrants are usually too busy being your whole army to babysit anyone.