Switching to a whole foods (or mostly whole foods) diet is definitely the best long-term thing you can do.
We are making a diet plan in the wiki, so far there's one week, but it should give you a good idea.
Nutrition for each day (and for each meal), the estimated cost and the time required is all included.
wiki/index.php/Vegan_diet_plan
If you do give it a try, let me know!
Besides that, focus your main calories on staples such as legumes and whole grains.
If you want, you see a classification of the best staples per calorie here:
wiki/index.php/Common_Whole-food_Staples
Beans, peas and chickpeas are always good, and things like whole-wheat pasta are very versatile.
Your staples should be the main part of your diet, then make sure you add in your vegetables (carrots, dark leafy greens, cruciferous vegetables, sweet potatoes, are all good), and some nuts/seeds and fruits as a snack or in the morning (things like peanut or almond butter, sunflower seeds, some fruits in the smoothie).
However, fruits shouldn't be a big caloric part of your diet, as there's heavy diminishing returns after you eat a few of them (they have important micronutrients, but poor macros). For example, a banana with a couple of fruits and a handful of berries in a smoothie would be good, but I wouldn't eat more than that.
You can check a classification of the best fruits to eat here:
wiki/index.php/Best_fruits_to_eat
So, to resume, in terms of calories: staples (legumes, whole grains) > vegetables (carrots, potatoes, cruciferous/dark leafy greens) AND nuts/seeds > fruits (just some berries, and something else if you like fruits)
That's a good way to look at it, but the link I gave you above is a good weekly example.