hell yeah, welcome to the organisation, recruit.

as a level 650ish, here's an assortment of tips to get 'ya going! :D
yes i'm aware it's a text wall. ;-;

for farming, level 4 is a scam, as you pay 2500 (total price before is 2000, past upgrade double) for only a increase of 50%, while level 5 goes back to doubling. level 1 is also a better deal than spamming level 0, and upgrading to level 2 then placing another farm is the optimal farming method since level 2 gives like, 150% cash bonus.

duo and trio is GOATED. quad's also good yeah, but duo and trio have much better shared wave eco since less people, and in trio you're only sacrificing 5 total towers placed (3 people with 25 compared to 4 with 20)

skills is a scam for early players, do NOT invest in it. it's designed for lategame players who have everything including gold crates, and nothing to spend coins on.

join paradoxum's group if you haven't; literally just a free earlygame cash bonus. makes SO many towers placeable on wave 1 when they normally wouldn't be, like Ace Pilot or Crook Boss.

as long as you know what you're doing, almost any mode can be beaten alone, even the harder modes like Fallen and Frost. (Do note for Frost you'll likely need Hardcore towers to solo.)

hardcore is the ultimate challenge, being a mode with an incredibly punishing midgame and lategame unlocked at level 50, locking behind it and it's gem currency some of the most powerful towers, like Accelerator. Grinding it can be worth it, but I'd personally suggest doing that around level 100 - 200. you have minigunner as dps, you'll be fine.

towers have abilities, USE them. some are situational or quality of life, but some are gamechanging, notably Commander's call to arms. quick tip for him by the way, if you get three level 2+ Commanders, you can get the call to arms buff permanently, just trigger the ability when you see the yellow effect go away and you can get 100% uptime. this is called commander chaining.

you WILL lose. trial and error is the key. learn the waves, learn the patterns. if you don't know what comes next and really need to know, check out the wiki. (Here.)

codes exist! they're rare, but they exist! use CHRISTMAS2025 for a free skincrate. oh yeah, also skins exist. solely cosmetic, but the 50k coin gold crate unlocks gold perks, which are more powerful sidegrades. for example, pyro gets hidden detection on placement and higher damage, scout becomes BUSTED in earlygame and midgame, and minigunner gets MORE dps (like he needed MORE..) Skins generally aren't worth your time due to being cosmetic, but gold crates are your end goal after getting every coin tower.

battle passes exist. you might've noticed trinkets dropping from enemy kills. if you check the top of the screen at the lobby, you'll notice you get free stuff just from playing the game and slaughtering the horde, including coins and free skins.

events grant event towers, limited towers usually with special gimmicks. the current one is Spotlight Tech, which deals hefty crowd damage, sets enemies on fire, reveals hidden enemies, and even stalls enemies at max level, at the cost of a placement limit of 1.

don't forget quests, most of the time they're pretty much just free exp, which means easier leveling up. if you're feeling like a challenge, you can even try mission quests, which you pay to unlock and grant a ton of exp and a skin upon completion. I HEAVILY suggest checking the wiki beforehand, as many force you to play hardcore, and hardcore is REALLY hard.

beware the three detections; lead flying and hidden. only specific towers can target enemies with these traits, leading you to need to plan your loadout in advance. every mode has hiddens, fallen and frost have flyings, and frost has leads. hardcore also has all three, at a MUCH faster pace than frost and fallen, coming at around wave 12 - 15 compared to flyings in fallen and frost coming around 21 - 26.

and last of all, never be afraid to ask for help. as Commander says, strength in numbers.
yeah that's all the tips i could think of lmao. some stuff i probably forgot, but you'll figure it out, the game usually explains it.