One way to run the 'Nids is as a giant "Fist". You place your termagants in front, right on the edge of your deployment, then Hive Guard behind, and your Tervigons behind those. Essentially, this creates a cover save for each of your units, as gants will screen Hive Guard, the Hive guard cover 50% of your tervigon, and the Tervigon provides
FnP to the gants, making target priority very cyclical and difficult for your opponent.
On one hand, the termagants are going to be nasty in close combat if you don't kill them off, due to Tervigon buffing (please for the love of god give him adrenal glands&toxin sacs). On the other, the Hive Guard are going to
de-mech you fast if you don't kill them. But they're T6 W2 and have 4+ armor/cover, so they're not going anywhere fast. On the other other hand, the Tervigon is making your termagants pretty darn powerful, and if he's nearby, he can make your termagants able to decommission a rhino with s4 on the charge.
This is the basis of most lists I play; however I recently experimented with zoanthropes walking up the board in front of the termagants, and I'll say it's oddly effective when paired with the dual threat of 3 Mawlocs turn 2 in your backfield.
One thing you must learn about nids is nobody knows what to shoot (except
DE who are threatened by whatever is closest to them, as even fleshborers can glance a venom/raider). The psychological game of "I have 3 mawlocs (or trygons, or zoeys in a pod, or outflanking stealers, etc...) coming up turn 2 in your backfield and there's nothing you can do about it" paired with 100+ termagants backed by a few Tervigons making them awfully durable, and being very aggressive with whatever your preferred anti-tank is (zoanthropes in my case), can really scare most of your opponents into awfully bad decisions like clumping up their tanks or spreading their forces too thin. 'Nids are really a unique threat that, unlike what most people on Dakka will tell you, are actually an amazingly powerful and synergistic codex with lots of choice between multiple different heavy hitters in every force org slot.
As to your current models; Warriors are nice as extra synapse, but I don't usually recommend running big blobs of them, as they easily become obvious targets. Run them in groups of 4-5 with your preferred gear, covering your tervigons, allowing your
HG to get a little closer, or be placed on the flanks. You want your little gribblies swarming forward, and the added synapse on the flanks or in front can help you get up towards squishy things like guard blobs fairly easily.
One issue with Carnifexes is where you deploy them. Podding them is too little too late, and they can get in the way or out of synapse very easily. I like them - but run them with 2x3 Hive Guard and maybe a group of Zoeys (more for the ap3, not the lance, but your opponent doesn't know that). They also don't particularly offer anything new or exciting that we don't get more viably elsewhere, like Mawlocs, Trygons, or T-fexes. And despite being a T6 W4 3+ Monstrous Creature, they go down pretty easily, and can be pretty disappointing. However, if you plan on fighting a lot of Necron AV13 or Dark Eldar AV10 spam, Heavy Venom Cannons are actually amazing, as their open-topped negates the worst part of the
HVC (the second being that it's 1-shot and scatters), which still stinks.
Genestealers in my experience are amazing as outflankers, and not horrible as infiltrators, especially if you're infiltrating out of
LOS within their table sidde/quarter because they weren't careful. Just take care not to let them assault speed bumps instead of the really juicy things like Russes, terminators, etc. Try multi-assaulting if you can, but also be careful of getting unfortunately tarpitted, like I was one time against 2 grots who held up my 'stealers in assault for 4 turns. Ymgarls are nice, but unless you want to go for a ballsy strategy like massive stealer shock, I'm not recommending it over your shooty options in the Elite slot.
Most people I know model their Hormagaunts with fleshborers/devourers and call them termagants, because hormagaunts aren't considered very amazing, but with a Hive Tyrant, you can make those babies outflank, and threatening them with 90 attacks on the charge coming from 12-18" from either board edge will get your opponent nice and clustered in the center like you want them to be. Just remember, they're not as good as termagants in Tervigon buff range, but you really don't need synapse - they're gonna do exactly what you want them to do outside of synapse anyways. In my opinion though, their upgrades are way too many points - I could have 2 hormies with Adrenal glands, or a space marine who could shoot them AND has the "all 4" statline to boot.
As a 'Nid player, just remember that what you do in the list-building stage will determine your entire game plan, and while most lists will appear pretty similar, they can vary wildly in function. 2 T-fexes and Hive Guard is a much different threat than 3 Carnifexes and Zoeys in spores, which is different than Zoeys and Mawlocs, which is different from 9 Carnies etc... Your main variance is coming in through your Heavy and Elite slots, where you get your fun toys. Troops are for gribblies. Fast attack is nice, with Gargoyles or Raveners both being relatively good choices (I prefer gargoyles, auto-wounding on 6's paired with a Hive Tyrant can get them a lot of auto-wounds, but raveners can be nice with rending claws, making them kind of like faster Genestealers). And don't be afraid of putting one of your (please have 2+) Tervigons as an
HQ to save points. Trust me, you don't need 3 scoring
MC's, 2 will do just fine when you have 100+ termagants, and I never understood why people thought spending 80 points on a Prime to make one more redundant tervi scoring was "saving" them any points...
My list suggestions would be buying 2 or 3 Tervigons, lots of termagants (~100 will be good, just hope some die turn 1 or 2 so you can keep spawning), and some Trygons/Mawlocs (honestly doesn't matter as they're the same size, get whichever is prettiest and just tell your opponent "this is a Mawloc/Trygon/Trygon prime"). The models are awesome, and you'll find yourself running them almost every game. You may want to also purchase/proxy any of the other units I mentioned; Hive Guard or Zoanthropes should be a high priority, and maybe a Hive Tyrant and some Tyrant Guard. Biovores are fun to play with, and are a single unit that will negate the viability of Green Tide against your list entirely, whilst also not being too awful against
MEQ.
My final advice is to experiment with literally every single unit in the codex and see what you like and don't like about them. Harpies have done wonders for some players, but I can't justify the points when I could get gargoyles instead, which do much better in my experience. Podding zoanthropes has done miracles for some, but every time I do it, they get a bad scatter and Perils and derp their invuln save. Hive guard were awesome for my friend, until he used a lone T-fex and it actually blew up its points worth of rhinos and marines while the hive guard couldn't figure out which end of the gun to point at the enemy. The Hive Fleet is always adapting; so should you. Proxy stuff until you like how it works, and if you end up buying the models, you may have to adapt your strategy to fit the sheer size/shape of them (I know I did when they released the actual Tervigon model, which is beautiful, just massive). Play lots of different opponents, competitive lists like
BA mech,
IG mechvets/Leafblower, Space Wolves,
GK pallys,
GK purifiers, Necrons, Kan Wall/Orks, and
DE venomspam, and you'll learn a lot about how you deal with each of those different threats. Well okay, they're not different at all because 5th ed transport&mech metagame, but you get the point. It's also good to play against more fun lists, like an all-scout Marine list, all-Grots, 84 Fire Warriors, and whatever other crazy stuff your opponent can come up with - it will help you learn just what your units are capable of, what they can do, how terrain effects your strategy, etc.
I can't force you to play the same way I do, and am only offering what I know of the codex after playing it for a year and analyzing each option in the codex, and playing against the best generals using the most competitive lists I can; I can't be sure that you'll find the same units effective as I do, but I promise if you really sit down and look at the codex for a while, things will start making sense, and you will start seeing some interesting links between units that might not be obvious on the surface. Make your hive fleet your own vile creation, and relish every single grimace your opponent gives when he loses yet another unit to your swarm. Oh, and grimdark grimdark.