I recommend getting familiar with chickpeas and tofu. They are both very cheap, very filling, and very nutritious (chickpeas in particular, once you learn how to reconstitute the dried ones). Experimenting with recipes that involve those ingredients is definitely a good idea. Learning to cook quinoa and rice is another helpful skill (wild rice is also nutritious and filling, and quinoa offers a complete protein). Working with those four ingredients and mixing in other vegetables, spices, mushrooms, sauces, etc will offer a very wide range of delicious and nutritious foods that you can make as a baseline.

You can also look into the dishes of different cultures that have vegetarian traditions. For example, Indian food has a very large range of interesting vegetarian dishes. So does Taiwan, and other strongly Buddhist-influenced cultures. In Japan, Buddhism-inspired vegetarian food is referred to as "Shojin-ryouri", so if you like Japanese food, you might look up some shojin recipes. Those are just some examples =)