I was raised as a Hindu. I'm an atheist now.
One major difference between Hinduism and the Abrahamic faiths is that Hinduism doesn't have a central authority, like a book or an official church. It is mostly made up of rituals and traditions instead of a philosophy to build your life around. As long as you follow the rituals and tradition, you are a Hindu.
You can't "convert" to Hinduism as no such concept exists in the religion. The reason for this is the belief that God knows best and since he birthed you into a Christian/Muslim/other religion household, the best thing for you is to follow that religion. That basically means that if you're Christian, the way you can be a good Hindu is to follow Christianity the best you can. Which might sound bizarre to some people, but it's true.
But then, since there is no central authority who can say that you can't "convert"? There are people who don't mind converts, there are others who think you have to be born a Hindu.
The underlying foundation is the concept of "dharma". Which means righteousness. As long as you're righteous, you are a good Hindu (regardless of the religion you follow), in philosophical terms. In real terms, as long as you follow the rituals and traditions and celebrate the festivals and go to a temple every once in a while, you are a Hindu.
Being righteous means doing the right thing. What the "right thing" is changes with time and the mores of the society.
It really doesn't require much effort. People would consider me Hindu because I was born in a Hindu family, but I am an atheist and don't pray or have faith or anything.