This is the standard runeset. You need that extra damage for the pressure usually
Starting e or q depends on the lane but if you think the enemy wont try to all in you lv 1 going e gives you an easier time farming. I put 2 points in e level 3 usually unless the speed is necessary as it helps me push the lane faster
This is what i usually have the most impact with and get the most value off in lane and in a 1v2 when enemy jg comes. Also the shroom cdr is good lategame combined with build you can get one around 8-9 seconds
I really like starting Dark seal and refillable. It doesnt give you the stats that DRing gives you but it has better sustain and it allows me to snowball easier if i play better. If you dont feel so confident DRing +2 pots is ok. Against something with more range and poke i suggest DShiend so you can survive the lane farm up and just get in the midgame with somewhat even gold.(Kennen,jayce,rumble etc)
Early game
Item choices
Dorans ring + 2 pots is good into anything, a solid choice that can lead to you getting an early first blood. Dark seal + refillable is my go to because i want to snowball (as teemo you have a big chance of getting that first blood or just a kill in general in early levels)and also the refillable does help everytime i back and i back very often. Dorans shield + pot is when you think you wil be abused and poked and you just want to survive laning phase. Combo it with second wind as well so you can take a few minions but not get poked to low enough where you are divable.
Teemos early game is good but also very vulnerable especially now that the river to gank top is bigger. You always want to try to get a cheese going if you can get 100-200 hp from the enemy at the start of the lane that gives you so much pressure on them in the early minutes. If the enemy is something like darius,tryndamere that want to chase you down level one starting q and then w second is very good because if they get you low they can try for an early trade and crash the wave under tower. If the enemy jungler starts botside you want to only last hit the first 2 waves while poking as much as possible and then when the third one comes you shove as fast as you can, back spend gold and either contest the scuddle or just ward the river bush and let the wave come to you. Teemos kit makes it so you want to be pushing the enemy under tower and either hit the tower if they play passive or if they keep trying to walk up just punish them for getting the caster minions. If the lane is hard you just want to farm and scale for the midgame and try to group up with the team when you see a fight possibility so you can get some gold away from your laner. Also shoving gives you an opportunity to group with your jungler and get the new rift monsters for a little bit of gold and true tower damage so call the jungler and set up for that.
Losing Mid Game
Teemo this season is one of the best scalers into the lategame. If its going badly (they keep diving you, you are a few kills and levels behind)all you want to do is get gold wherever you can find it. Go get some gold on other lanes try to get a kill mid or bot or just a dragon to scale up a bit better. Even if your lane opponent is getting something done top its ok because you cant stop them anyway. Try to get farm maybe jungle camps and swap lanes if possible with someone strong enough to stop your laner so they can cointain them while you farm up. Communication with your team is very important.
Even/Winning Mid Game
Usually around the time rift herald is about to spawn you should have done a lot of damage to top tower or destroyed it if everything went well. So call your jungler to take it and drop it top to finish tower or just go mid/bot and try to do something there if you already did get your top tower. Your priority in the midgame is to help your team by shrooming objectives and finishing all tier 1 towers in the map. Contest everything you can and if theres enemy shutdowns bigger than yours just try to get a passive in a bush or lane and flash ignite them.
Losing Late Game
If the enemy team has a better comp you cant really do much just get as many shrooms in as you can and stall for your team to do something or the enemy to do a huge fuck up. Try not to be the one engaging in your team because you have a lot of waveclear that is necessary if a fight goes badly If they dont really have a better comp just try to stall as much as you can for your team. Give objectives if behind cause fighting and losing that fight will put you further behind. Your whole objective is to bring your team into the game as when everyone is 6 items being 10/2 or being 2/10 doesnt matter(yes i know your botlane is 3/34 but if they get to 6 items its all the same).If theres a dragon or baron in a few seconds and the enemy look like they want to go for it try to do a push on mid or opposite lane to get some gold and just neutralise enemy pressure on that lane. (sometimes can get a full tower or inhib). By this time your shrooms will be 8-9 seconds and very deadly so the enemy usually gets 4-5 sweepers and they dont have as much vision which makes it easier for you and your team to get into good fights
Winning Late Game
If you are severely ahead try to get your team to push and get every objectives so you can stay in the game. If enemy has a splitpusher you stop them yourself or if theres a mid or adc that is relatively weaker than you you send them to stop the split and you stay with the team and keep pushing to their nexus. Time is most of the time against you cause the more it passes the weaker you become related to the enemies. Try to get everything in the map and not let them get out of their base to get any gold without punishment, shroom deep into their jungle, set ambushes with the support or jg while someone else pushes anything cheesy that you can just to stop them from getting gold and keep your team pushing those objectives