You are a ranged Nasus, so your primarly goal is to stack your Q. Unlike Nasus you continue to stack in case you need to use abilities on enemy champions.
Early Game
Early game focus on stacking your passive and Manaflow Band, but avoid any trades with anemy champions without your W as well as extended trades. Smolder isn't great at auto trades with enemy ADC.
Once you hit 25 stacks of your passive start maxing your Q and continue to setup 3 or more minions to die at the same time from a single Q. This is especially easly to do against caster minions. Continue to farm, farm and farm. Don't chase around enemies, they will come to you instead or leave you in peace to scale safely.
3 Item Powerspike
When Smolder gets to 3 Items he will likely have a lot of stacks and many enemies will underestimate his damage as well as tankiness. The fed enemy ganking you might expect to kill you as easly as killing a standard Crit Smolder only to be suprised how tanky you are and you end up surviving or even winning the fight. At this point it is not uncommon for a few people to get baited that way thinking they can 1 vs 1 you. If things don't go as planned E is a great escape tool, especially when used over walls or on the edge of the map.
Lategame - 225+ stacks
As you buy more defensive stats and CDR, Smolder continues to stack his passive and stacks faster and faster the more stacks he has already. In pvp continue to spam your Q, while kiting back in between Qs. I repeat DO NOT stand, while auto attacking. Q, run back, run forward, Q, run back, run forward, Q...
While Smolders burst damage will be smaller than in his Crit builds, he will be able to fight longer dealing the damage over longer period of time as well as getting more stacks from the aoe Qs. Crit build Smolders often get shut down during this stage by simply being bursted down by a mage or assasin, but it is much harder to do in this build.