Tips for becoming a player who can solo T3's?

the ranking on this site of the difficulty level of Level 3 solos is accurate. https://pokemongo.gamepress.gg/tier-3-raid-solo-guide

Of the current batch, forget Ninetales, impossible without perfect lineup, though weather now makes a big difference. Machamp is totally doable because there are several great psychic attackers. And Machamp is VITAL to beating TTar, Blissey, Snorlax, Lapras. Basically you want and need Machamps!! A perfect Alakazam will be worth powering up, make sure he has double psychic moves. Eevees around here are very common, when you find a high IV one start walking with it, do 10k (2 candies received) and make sure you then evolve it, while it is still your buddy, during the day, that gets you a great Espeon. A double psychic Eggy can be used, Mewtwo obviously. You need a full lineup because Alakazam and Espeon do huge damage but they are glassy. My last one I still had 25 seconds on the clock, but I had a 3400 Mewtwo in there.
Gengar is easy, again using psychic types and of course TTar.

You might post a screen shot of your top 12 by CP or just tell us what you have there (if you are 29, than 93 Ttar may be ~3000 but is it B/C or B/SE or maybe it’s still ~2500 with IT/FB??? You may get some good leads along the lines of “you can probably already do porygon” or “find an exeggcute ~L30 and evolve it regardless of IV and then use it and X and Y and Z and you’ll be able to solo ...”

Gengar is the easiest t3 to solo imo. If that 93 iv tyranitar is 15 attack, I would invest dust into it. It would help a lot with gengar and especially alakazam. Alakazam would be on the harder side of the fence to solo. U would need to be higher level and need very good pokemons or high level banette with sc/sb against pc/fb. For gengar, I would go find level 30 35 eevee in the wild and walk them to turn them into espeon. Confusion futuresight is the moveset u want but it's not a 100 percent must if u don't have tm. U can also use those espeon for machamp raids. Level 34plus espeon with 15 attack hits a breakpoint for confusion against machamp and gengar. No dust needed on espeon to solo gengar s and machamps. U can solo omastar with level 30 plus double grass exeg. Go find level 30 35 eggs in the wild and evolve. U need bs/solar for moveset. U can use other grass.types too but eggs are 50 candy to evolve and best grass. No dust needed here either. Scyther is very easy. Use flareon from the wild, double rock golems if u have them or ur tyranitar if it has bite stone edge. Porygon is very easy too. U can use.machamps from solo raids or u can use ur espeon army if u want to.

Don't stress about it if you can't do them. There's nothing particularly rewarding about soloing when you're spending so many resources towards a short-term goal, rather than a long-term goal.

Learn to use the raid analysis feature on pokebattler.com, and create a free account which will let you input up to 50 of your pokemon. Then, you can see how close you are to being able to do various raids, and which pokemon are the most efficient attackers for the various bosses. Also, learn how to use quick-move breakpoints to allocate your resources (candy and stardust) efficiently.

I'd suggest picking a single T3 raid boss to focus on, and try to optimize your team for that boss. Porygon and Scyther are by far the easiest. Fighting types (especially Machamp) are strong against Porygon, as are Espeon and Alakazam. Rock types (especially Golem) are very strong against Scyther. When you can do one of the bosses, move on to optimizing a team for the next one.

Also, try to make sure you use your free raid pass every day. Until you can do some T3's, do T2's or even T1's, if it means not letting a raid pass go to waste. You'll still have a small chance of getting a TM, and you'll likely get some useful rare candy and golden razzes.