It may surprise you, but you can pick Ekko in almost every matchup, some may be tougher, some are easier, but you can take it, and win if you know your champ', and if your support trusts you. Just try to avoid him whenever you see a black-shield in front of your or Blitzcrank. I hate Blitzcrank. Do someone actually like Blitz' ?

The game has just begun, you are level 1:
Farm with your Q, dont try to poke with auto, it's too dangerous. If the ennemy takes too much time to go on lane then try to get to Lv2 as fast as possible while staying as safe as possible.

Level 2~5:
You hit your first powerspike, you can deal a ******* lot of damage if you time your Q ---> E correctly with your support to help you poke.
If you lose the trade, then don't try to force those kind of fights until level 6, if you win it, or even kill, then repeat as often as possible.

Level 6:
You hit your second powerspike. Your R deals a ton of damage, so try to time it correctly to or finish an ennemy, or try to bait it with your clone to grab him them one tap combo.

Ekko isn't a great farmer at botside because of the difference in range, just try to get the most kill possible by roaming and waiting with your sup' in the ennemy's jungle. Try to go in every teamfights to and kill squishies with your combo, and finishing ennemies nor leaving with your R.
Your objectif is not to get the most farm, it's to stomp every other lanes.

Try to poke with Q ---> E ---> Auto then go back, it will proc' Electrocute and your passive, dealing a lot of damage.

If you are losing your lane, wait for your support or jungle to make you an opportunity to get kills, dont force it yourself.

Your R deals a ****ton of damage, while being OP: you can dive safely by going underturret without attacking, then go back behind your minions, W on the ennemy ADC, then wait for your clone to be in position then R and it's a free kill.

If you are fighting Blitzcrank or a BlackShield, I have only one tip: Have a burst sup' or FF.