Teemo is no real damage dealer. Hes a off-supporter.
Ur job is blinding the enemy ad carry, counter the jungler, bring map awareness, push turrets.
Madreds and Frozen Mallet are ur Core-Items so watch out that u got them quite early.
Teemos positioning can win teamfights. U sometimes need to tank and sometimes u need to nuke anyone. The right choose in every teamfight is the thing, making a good or bad teemo out of u.
To play teemo right and to get enough farm is not that easy, so as a newbe i wouldn't follow this guide coz its quite complex.

Bringing ur enemy(jungler, ad carry) rage, be a undestroyable Monster with cute rabbid ears, thats what u get tought in this guide.
I prefer solo lane, but u can take every lane in game.

The great thing on teemo since his lil remake (with the movespeed buff) makes you to a extreme safe backdoor and pushing char. all the time u got some free time and no fight is in sight, u should be on a lane and grab the farm. use ur shrooms to safe urself and build escape ways.
Try to get a redbuff(for example counter enemy jungle)

with 15% more attackspeed u will be able to have a nice dmgoutput in the early. with ur early 15 ap runes ur dot will be horrible for the enemy so use it wise to harras' ur enemy(ies).
ur life per lvl runes will support u in the lategame.
Ur cooldown reduction runes will help u to place more shrooms( combine those runes with a bluebuff ingame)
Health per lvl runes make u very tough in the lategame. U also can use Magic resist runes, u can make 2 rune builds and u can decide, after u saw enemy picks.

it is extremely important to take teleport at the toplane, because after a gank u will be able to defend the turret. also u can make a teleport gank at any ward on a lane to surprise ur enemies.
Flash is a musthave today so take it with every char.
On a duallane take tp(if u want to get more chances to backdoor) or take ignite and flash.
ignite can be a real execute for ur enemies, with the dot its extreme usefull.

Get ur Core items early. => Creeping
There can be games where u need more dmg items coz of bad picks. Thatfor i would recommend wits end for resis, attackspeed or a bloodthirster for some burst combined with sheen.
With ur shrooms and ur mallet u can kite ur enemies, till ur teammates arrive, play clever and frozen mallet will take place in ur heart.

For resis u got armor of madreds-madreds and u got magic resist by ur boots. with frozen mallet u get enough life. with ur late GA u will be very different to kill, tank ur enemies if its needed, u are built that for.
Its very important to have a madredsrazor effect as a counter jungler. Ur lantern will give u back the effect, when u updatet ur razor to bloodrazor. buy the lantern whenever u need it(u also can buy it before bloodrazor and phage, it really can help u at toplane)

U buy madreds and u make magic damage with all ur skills. eneough reasoning to skill archaic knowledge to push ur dmg.
In your items there is no life reg. so skill strength of spirit. in the lategame u will have enough mana thatfor u rly see the differents between skilling it and not.
U can skill a faster teleport but i think its not that sensefull

with ur poison its extremely easy to kill minions. stay at the 15 mins 100 creepkills (in the end of the game, teamfights concluded) to buy early that good items. ur shrooms give u a lot of sight and a lot of safepaths to be a perfect backdoorchar and to counter jungle. use them right and u will help your team to have a easy win.
on lane just farm, harass' em up and rezone ur enemies with auto atks.(if u are able)
farm is the most important thing on teemo!!

Very important: guarant ur team sight to enemy buffs.

(black points shroom places. if u want to go backdooring/pushing turrets, make safepaths like i for example made in mid)

in rnked games it is extremely important to play together with ur team and take those roles they give u. with teemo u can hold top lane, mid lane and u can play at bot lane.
In rnked games watch at ur farm and try to have about 100 creepslains in 15 mins.
As teemo u are a real good counterjungler in the mid game. place ur shrooms to get some map awareness in the enemy jungle. The better map awared team will probably win.
In rnked games ur enemies won't concede(surr) that fast in the most of the games, that team that pushed the better way wins. use ur teleport to take a turret, if ur enemies ignore creeps on a lane.

At first skill ur dot. There are many reasons in that guide.
To skill ur blind will give u some burst dmg. (u can buy sheen more early, if u need some burst damage.)
look up for lvl 6 and 11 and 16 and skill ur shrooms. hold them on cooldown.
ur movespeed isn't that important. skill it on lvl 3 to have a movespeed advantage.

with these items, ur positioning is extremely important. If u are a new player, play another guide, yes its quite difficult.
ur dmgoutput isn't compareable with a malza or a gragas, but u really support the team with the frozen mallet, the pushes and with ur blind on the enemy ad carry.
Ur survival is nearly guaranted with these items. u are able to tank ur enemies and to kite them.
It rly will help u to have a bluebuff all the time, i wouldn't say u are a bit dependet on it but its really important.

Farm, Push, be thoughtfull, kite ur enemies, bring ur enemy rage, take the enemy ad carry out of the match. U can decide every clash, u are a supporting role.