I learned a few basic templates from my wife. I don't have specific books or sites to recommend, but a general "approach" that you can use when looking at various resources (online or in books).
There are two or three templates that you can use with different base components to achieve a wide variety of dishes without a lot of memorization.
For example, a basic north-indian vegetable dish template I use is simple. First, chop an appropriate veggie (green beans, potatoes, beets, cauliflower, etc.). Heat cooking oil in pan until it's hot enough that mustard seeds start popping when you add them. Add a handful of mustard seeds and while they're still popping (within 5 seconds or so), add the veggies. Dry-cook that until veggies are cooked to taste, add red chilli powder, optionally some mustard powder, and salt to taste.
That template basically gives you half a dozen dishes that taste very different depending on the vegetable.
Likewise, there are simple templates for dals - typically you prepare an onion-and-spice paste by heating a small bit of cloves/cardamom in oil, reducing the onions down to a post-caramel paste, spice that with cumin and coriander and red chilli powder during the reduction, and add some tomato chunks towards the end. Then take the spice-onion paste + semi-cooked tomato chunks and add that to water and dal and cook in a pressure cooker (or regular pot if you're willing to soak the dal overnight prior to soften them).
There's a similar approach with an onion-base curry paste for meats and hardboild egg curries.
I didn't learn from books myself - mostly experimentation and getting the hang of a couple of basic templates which I started experimenting with. Personally it's more enjoyable that way.
But whatever resource you use, keep in mind that you can have a _very_ free hand in experimentation, substitution, and alteration. There is no orthodoxy and Indian cooking varies from area to area, village to village in specific choices of ingredients and spice mixtures.