You could buy accounts with Karma already intact and spam it yourself. Problem is, if you spam too hard Reddit will ghost your account and you'll be the only one seeing your posts (this happened to me once with a throwaway account).
The best way to leverage Reddit is to interact with the community. But even if you spend time hamming it up with them, the Redditors will still flame you when you post something even slightly promotional. If you have some genuinely useful content then you might be ok. Like if your niche is fly fishing and you have a really good article about the best type of flies to use, then you could get some traffic and upvotes.
I only post to Reddit when I have something really good to say.