When I was in my late teens I started thinking about a lot of things more objectively - you see I really internalized the idea of being a "truthseeker" from the cult, I guess I just missed the point that truth=cult. I was also in college getting a degree in computer science engineering at the time, so I was taking a lot of courses on logic, statistics, etc and got interested in rationality and logical fallacies. I learned how to spot logical fallacies and started seeing them in every theist's argument for the existence of god. Usually taking the form of special pleading, appeals to authority or appeals to consequences. When I thought about this stuff I often found myself thinking "If I weren't a JW I'd definitely be an atheist" or "If I hadn't been born into being a JW, there's no way I'd ever become one." Unfortunately life got in the way and a few things happened that caused me to fall back into the cult mind control for another 10 years or so, but if I'd been honest with myself, I'd have become an atheist back then. Once I woke up to the mind control of the cult, I wasted no more time with theism.
If you're really interested in finding truth, I'd start by learning how to really be rational and how to beat the in-built biases that we all have that make us tend to be irrational. Here's where I'd focus:
Learn about logical fallacies. This wikipedia page is a pretty good starting point: https://en.wikipedia.org/wiki/List_of_fallacies As you learn about these, try to spot places where you have in the past or where you're still relying on one of these fallacies to justify some belief. You don't have to look at your belief in god to start - the more invested you are the harder it will be to attack a belief, so start with small things - maybe little bits of trivia that you've never verified but you still tell people, etc. Many people, when learning about logical fallacies, learn to apply them to other people but still have a hard time applying their new skill to their own beliefs - don't fall into this trap. If you do this, you use rationality to make yourself stupider.
Actively try to find places where your beliefs are wrong. Again, maybe don't start with religion...maybe start with some political view that you're drawn to but aren't very invested in one way or the other. Research the counter arguments for what is your gut feeling. Make arguments for your stance and then pick them apart as though they were another person's argument and you are arguing against it.
When you discover that you've been wrong - celebrate! Shove aside the shame that we all instinctively feel when we find out that we've been wrong, and instead celebrate that you're now wrong about one less thing. Everyone everywhere is walking around with at least one wrong belief, and being wrong feels a lot like being right...it's when you find out that you've been wrong that you feel bad, but that's precisely the moment when you should celebrate your success. This may seem like a little thing, but I suspect that a great deal of people's irrationality about things stems from a fear of accepting the shame of having been wrong. If you can eliminate this feeling of shame from yourself, you eliminate a large source of bias.
Learn about Bayesian inference. This is a remarkably simple, but extremely powerful tool for coming to accurate beliefs. This is a method of essentially assigning a probability for the truth of an idea (its credence) and then updating based on information. It's a quantitative tool, but just having a qualitative grasp on the idea is very helpful.
If you want to challenge belief in god directly, there are lots of good books out there, one that many people have found helpful is Richard Dawkins' "The God Delusion." For a great (but long) primer on rationality, I can't reccomend Eliezer Yudkowsky's "Rationality: From AI to Zombies" enough. It's long and delves in to a number of topics that are a little bit more philosophical, and it spends a fair amount of time on discussions of artificial intelligence, but I found most of the diversions quite interesting as well, and they were typically still very helpful as metaphors.