A few possible factors here:
1. Have I been slighted by God? If so, I would arrange for top grade military equipment and train up an army to invade heaven. I imagine I would already have some great leaders and military personnel on my side, regardless of their morals, from Hitler to soldiers who committed war crimes or beat prisoners of war. And the rest would be fast learners, faced with eternal damnation otherwise.
2. Am I merely out to annoy God? If so, I would make Hell better than Heaven in every way and make sure the most dastardly of sins are rewarded by only the greatest luxuries. Forget the pearly gates, we shall have gates of gold, or chocolate, and bacon shall come free with every meal. Proper bacon too, not that striped crap. And the ceiling shall be shatterproof glass, such that all in heaven may look down and constantly be reminded of what comparatively poor conditions they are in.
3. Am I a dick? In this case, I would be punishing sinners eternally, which is the standard approach. The setting would be a standard city, except that it is impossible to sit down and everything is boring. No food would be provided, although hunger would still be in effect. I would install a one-way glass ceiling so that all of the inhabitants of hell could look up at heaven and see what they were missing out on. They would also have random limbs paralyzed without warning or explanation, if possible while they are being used, and would have constant sin-specific punishment. I would also spend most of my time devising other one-off punishments, to occur randomly over the course of eternity, such as a waterslide with no water, a rising water level and descending ceiling at the same time, endless steps or an endless queue, being substituted for Pacman in a game of Pacman, having to count a mountain of rice with only hot tweezers (only the right answer will end this treatment), being placed on a conveyor belt that extends over a pit of decaying flesh and bugs (the belt gets gradually faster and is relative to the person's fitness), playing a video game where you are killed right at the start and your respawn timer never decreases, being placed in complete darkness with only an invisible mosquito, having to recite a list of every Team Fortress 2 hat ever made in order, and having a bug placed under the flesh that cannot be extracted until the treatment is over. If I was feeling bored, I would send some of them back to Earth in positions where they were able to commit the sins that had them sent to hell in the first place.
4. If none of these are in effect, I would simply judge people myself based on all their crimes and any mitigating circumstances, people who simply didn't believe in God or maybe worked on the 7th day or had sex before marriage, I send either to heaven or if that is not possible, to a small dimension similar to solution 2. Everyone else would be placed somewhere similar to the loading screens in Assassin's Creed games, except in the person's least favourite colour, and given no clue as to how long they would stay there. They would all eventually have atoned, at which stage they would either go to heaven or Luxury Hell. The time is according to the severity of their sin and their understanding of how evil it is. For example, committing euthanasia with good intentions would net you free passage, swearing in public would get you perhaps a day if it was not necessary or for comedic effect, killing someone would depend on their character, your motivations, and the manner of death. Original Sin would not be punished at all.