Keep in mind that your q can be used on both enemies, wards, friendly minions aswell as enemy minions, turrets and ofcourse monsters.

You might not have realised/known that the activation range goes up on your Q aswell as your basic attacks which means that after a bit of stacking you will be able to activate your q on enemies much further away than you could at the beginning of the game.

Your w is slow but if you use it to last hit a minion the snare will activate right as it hits the enemy/minion it kills and snare anyone within range.

You can use your E to take your allies into fights as without being picked off since they are hidden within and can't be targeted unless you come too close to enemies or they hit an enemy.

even though you can't always use your ult to kill enemies in your lane you can use it to kill/assist people in other lanes so keep your eye out for those opportunities.

I hope this guide helped even a little bit and I hope you will enjoy Senna as much as I have.
Have fun dudes. o/