So as I'm sure you're aware if you've played Gaslight Joker before he runs off of health, his abilities consume it, his Q damage and healing scales off of it and when his ultimate is active he runs out of it fast, REALLY fast.
Gaslight Joker was nerfed badly a short while back and as such between himself and Wonder Woman (the only two Enforcers at the time of writing) he falls short in the survivability department, but for those (Like myself) who prefer a more aggressive champion to play than our other option, Joker can be played to effect but requires plenty of practise to do it.
When you start out be prepared to lose, ALOT.


Stolen Powers:
So not a lot to discuss here, Vampiric Batman's Consume as it resotres more health than the standard Consume, though if you're still working at buying this Consume works about as well.
Secondly you'll want Shazam's Invunerability you'll want this over the standard shield as it restores 25 health per second it remains active, again if you are still working towards this power standard Invunerability is a decent substitue.


Skill Order:
First things first to ensure maximum survival at levels 1, 2 and 3 you will want Q - Fetid Cleaver (For Damage), W - Shower of Filth (For the Fear) and E - Ham Snack (For survivability) In that order. The reasoning behind this is that your Q is your primary damage dealing ability and heals you for a small amount making it a very nice balanced ability, the W provides a fear which if placed correctly will hit multiple champions allowing for a safe engage or escape and the W provides complete immunity from the next spell to hit you as well as a speed boost (good for escapes / safe engages).
You'll want to be maxing your ultimate Rat Swarm (R) whenever it's up I'm sure this is nothing new to most people, but I'll go into my reasoning for this further in the guide.
Second is you're primary Damage ability Q you'll want this maxxed as soon as you can as the amount of healing increases with each level and will keep you in lane longer when combined with your passive (Healing over time for each coin Galight Joker picks up), This ability has a short cooldown and absolutely chunks drones if you are following this build (One hitting them alot of the time).
The second skill you want to max is your E I max this over fear due to the fact that having one point in fear (W) already you have access to the utility of the skill which is the main benefit over the damage, whilst your E when levelled will speed you further (Up to 60%) allowing you to either get away or land that final Cleaver.
Finally you will want to split your remaining talents between W and your Passive depending on whether you need more Healing or more damage / Quicker Fears. If your team is win handily I might suggest levelling your W over your E first for the extra damage and push it will provide.


Items:
As mentioned before Gaslight Joker works via health and that is exactly what you will want to build towards here, any items that provide health and regeneration should be focused.
To start with you will want the first levels of Olympus Gambit, Ruby of Life and The Crime Bible. With these purchases you'll be granted a large amount of life and regeneration with which in early skirmishes should allow you and your team to come out on top and allow you to be more ballsy early on.
You'll want the second level of The Crime Bible early on to maximize its passive utility followed by Olympus Gambit level 2 again to make the most use of its passive generation.
The Medusa Mask will let you gain a portion of life when levelling up whch keeps you in lane and in fights longer.
The Ruby of Life level 2 will grant more passive health collection which stacks well with your Passive ability.
Next for a quick and cheap burst of life the Hawkmans Harness will provide you a bonus of 400 health for a cheap 1000 gold overall.
Kryptionian War Armour level 3 is something you cannot miss on Gaslight Joker due to the Vitality passive which stacks with your Q and your passive granting a frankly hilarious level of sustain whilst in lane.
Finally you just need to finish your items off, the Ruby of Life is first overall thanks to the resilience it provides, Next is the Kryptonian War Armour for the additional health and bonus move speed. Olympus Gambit provides a useful aura for your team as well as yourself, and finally you can max the Medusa Mask for the final 100 health and 10 regen.

With this full build you should have close to 4200 health at all times as well as fairly high regeneration and sustain. this will make you difficult to bring down when combined with your Invunerability, Consume and E, as well as the % health you regen from your Q.


Playstyle:
So when playing Gaslight Joker I prefer a Defensive style and suppliment this by supplying him a solid dose of health to support how i play.
With health as his resource you are only really limited to timers on your cooldowns and as long as you remain aware of opponents positions and your cooldowns you'll do fine. If possible Lane with a Ranged Damage Dealer of any type, Gaslight Batman, Cyborg or Green Lantern fill this role very nicely. Dont be afraid to put yourself between opponents and drones to zone them out, just make sure you have your sheild ready to mitigate damage, other than that coins and your Q will do the rest.
Initiate with your W when its up and throw your sheild up for a solid engage, but rememebr to only engage when you have backup, Gaslight Joker doesnt have the damage to even 1 v 1 very effectivly but can sustain and defend with the best of them.
Later in the game when you have more health and your ultimate at your disposal remember to only use your ultimate when you are sure you'll catch at least one person or the health cost will destroy you in a matter or seconds, if you can quick bursts with a Q in between should keep Joker topped up and enemies wary, or better yet dead.

I'll update this guide later after more playtesting, but if you bear these points you shuld be able to run Gaslight Joker safely and securely.
Good Luck and remeber to have fun, it IS a game after all. =D