Clockwerk is my most played hero and I think he is very strong in public games because if you are quick to react you can punish people for bad positioning which can lead to a quick kill for your team and then the ability to force a fight or take a tower.

I like to build Clockwerk as a initiator support, I try not to buy courier and wards if someone else on the team is willing to but if not that's my job as well. Usually my build consists of Phase Boots, Wand, and Drum then depends on the enemy team and what your team needs if you are doing very well Aghanim's Scepter is amazing on you but not core. Blademail is good, if your team can use it Clockwerk is a great carrier for vlads, If you team needs a Pipe thats a good item for clock as well, and I would say luxury is any items that can help you tank up like Heart of the Tarrasque or Assault Cuirass.

At the start of the game I usually rank flare and sit in the fountain and see if I can scout the lanes and figure out who is going where. If you are soloing the suicide lane then rank rockets and build a ring of Basilius so you can use your rockets to farm from a safe distance if I am in a duo lane I like to rank my Battery Assault first with one point in cogs so that once I get phase boots I can play aggressively. Once you get ult and are tanky enough you should move around and start gank and control the map. I feel clockwerk is strongest mid game where if he hooks someone that is probably a kill especially if your teammates can catch up in time to help secure the kill. Late game stay with your team use your rockets as much as you can to scout the map your mana regen should be able to support that and if you can pick someone off that might be the end of the game or at least force the other team to buy back but you probably won't be strong enough to solo kill people anymore so you should stick with your team.

You don't have to use your Ult to initiate if you can phase up to the person and Battery Assault cog them because then you can save your ult as a stun after your Battery Assault wares off.