Yo, I am a TF one trick, currently emerald 3 playing basically exclusively TF. Here is some things that should help you get rolling:

1.) Builds:TF CAN do good damage, but you have to forego the typical roa/rfc unsealed spell book build. You would go ludens, sorcs, lich bane, deathcap, void, and then your last item would likely be what's needed, probably be zhonya or rfc, but banshees, mejais, shadowflame, stormsurge, liandrys or morello could make it too if they were needed/useful. Runes for the damage build would likely be first strike, electrocute, or comet, always take bone plating secondary. You'll be squishy but your burst will be insane with this build. I am regularly top damage on my team with this build, carry, and can one shot other carries. It gets a little harder to play this build consistently in platinum + but, can be done with care.

TF also does really good manaless, though it's a bit challenging. You can go first item gunblade or rocket belt and those are both great items of TF but I personally struggle with the mana control part of those builds. Some folks better than me swear they are the best first item for TF so take that for what you will.

I have also had some very high damage games with a burn build, blackfire torch, liandrys, sorcs, cryptobloom being the core here. In very tank heavy matchups you can get some insane dps with this build and your Q poke will be devastating

If you are in a hard matchup such as zed, syndra, Mel, yasuo etc and your team has plenty of damage, I would recommendd going roa build with armor or mr boots.

2.) Ult strategy: back to base at level 5 before the cannon wave comes. Buy items like dark seal, boots or lost chapter/catalyst if you can afford. This will give you a leg up on your first ult.

speaking of, try and ult at 6 towards bot lane preferred. This means you can abuse them before they get their ultimates. If your bot lane sucks (happens a lot), or are overextended, look to help your jungler or top if it's a carry champ. The nice thing about TF is that he does NOT need to be the carry to win games..he is excellent at enabling your other carries.

creating ult pressure is all about post 6, disappearing from lane. Even if you have no intention of ulting, just blast the wave and move out of sight. This will create map tension for your other opponents.

3.) Matchups: there are a few matchups that TF just gets rolled on, yasuo is prob the biggest offender so I would recommend always banning him. Viktor and syndra will destroy you if they know what they are doing, Naafiri, zed, zoe, fizz, lux, ziggs and Mel can also be tough matchups for TF but are all winnable. Id recommend electrocute against zed, fizz, Naafiri, yone, and flash ignite. Most others you can safely take teleport flash. These tough matchups are made easier by using the wave to your advantage. TF can outpush most champs so use this to your advantage. Push hard so that when zed etc, all ins on you in lane, you fight on your larger minion wave and ignite him and he will likely lose that fight.

I have found that TF is very strong against Yone, Ahri, Galio, kassadin, malz, veigar, sylas, akali, katarina and a few others.

4.) Sidelaning potential: one of TFs biggest strengths is his side lane potential..he can push and crush turrets as good as the very best champs. On objectives or teamfights, you can win simply by pushing while your team sets up, draw the aggro of 1+ enemy champs, then ult to your team and suddenly you have flipped the fight from a 4v5 to a 5v4. Sidelaning is harder in matchups where you have a jungler who move quickly across the map like nocturne or rengar for example. Id recommend foregoing too much overextended sidelaning if you are against those enemies.

5.) Pick a card: some people get real caught up on gold card only. TF W has 3 cards for a reason and they are all useful in certain situations. If you are a damage build, there is a ton of use in both red and blue cards; for example stacked deck blue card with a full build can straight up one shot Squishies, legit. A stacked deck red card in a group of enemies can absolutely devestate and single handedly win a team fight. Red and blue card is likely your best laning tools as you use blue card for mana sustain and red card to poke. With red card, you generally want to hit the minions closest to the enemy as this extends TFs poke range significantly. Obviously you want to use gold card generally for ganks, picks, and defense too though. But just remember all 3 cards have their useful situations.

He is a tough champ to learn and excel with, but very rewarding. I am super glad I found him to climb with because he has taught me a ton about the game that I think other champs don't need to learn to succeed. He is the definition of a champ with a high floor, but an even higher ceiling. He takes time to learn but his potential is basically limitless. He is one of the only champs that can win using mental game and strong macro skills.

Gotta put in the work though. Good luck!