How to make crispy pakoras/fritters - In Indian cuisine fritters are usually made with besan/chickpea flour/garbanzo bean flour/gram flour. Add 2 tbsp of corn flour or rice flour with 1/2 cup gram flour while making the batter and the pakoras will turn crisp. OR
Add 2 tbsp hot (not warm) oil with 1/2 cup gram flour. Then add water to make the batter. Nowadays, adding hot oil works best for me.

How to make soft rotis/chapatis - Knead the soft dough well for 5 - 10 minutes. Let the covered dough rest for 2 - 3 hours at room temperature. This makes the rotis very soft. Adding little oil while kneading also helps.  Personally, I dont add oil. 
You can freeze the leftover dough in freezer safe resealable bags. To thaw/defrost, place the bag in slightly warm water. Excess dough can be stored in 4 or 5 separate freezer safe bags to make thawing easy.
Puree or finely chop green leafy vegetables like spinach/palak, fenugreek/methi, dill/shepu etc. Knead the chapati dough with veggies and enjoy healthier, nutrient rich veggie roti or parathas. Add ginger garlic paste, coriander/dhane powder or any of your favorite spices.

What to do with leftover rice - Stir fry vegetables like cabbage, carrots, capsicum with onions, garlic and the spices you like. Add leftover rice and enjoy a different meal altogether.  Add soy sauce, vinegar if you like Chinese fried rice. Also try this recipe of Bhakri, an Indian flatbread made of cooked rice.

What to do with leftover daal - Shallow fry medium sliced okra/lady's finger/bhindi in oil till crisp. Add sambhar powder and fried okra to dal and Bhindi Sambhar is ready with leftover dal. OR
Saute finely chopped onions, ginger, garlic, green chillies, aamchur or tamarind with little oil. Add this to leftover dal and Dal Fry/Tadka Dal is ready to enjoy.

What to do with leftover stir fry vegetables - Stir fry vegetables are usually dry. I use them in making cutlets/tikkis or bread masala or fried rice.

How to cook crispy okra - Frozen okra doesnt work for me. Pat the washed fresh okra/lady's finger/bhindi dry with a kitchen towel. Let the okra dry again for 4 - 5 hours or longer. Drying reduces the sliminess of the okra. Also, while stir frying okra, adding tamarind or kokam or lemon juice will reduce the sliminess. Personally, I use tamarind or kokam.

How to make soft idlis - The batter must be fermented well in a warm place so that the batter rises well. 
Another step is steaming idlis. Before pouring idli batter in the plates, make sure that the water in the cooker has started boiling. After water starts boiling, pour the batter quickly and place the plates in the idli cooker. This step is important or else idlis turn soft on top and hard at the bottom as rice starts settling down.

Adding Cashews/Kaju to rice dishes like pulav and cutlets/tikkis enhances the taste.

In Konkani Cuisine, shallow fried fritters of potato, eggplant, arum, etc. are made crisp using Semolina/Rava/Sooji as a crust. For a change, I tried Yellow Corn Meal (not corn flour) and I liked it. You can use semolina or corn meal for frying fish as well.

For stir fry veggies and gravy curries, garam masala is the most commonly used spice mix. You can use a variety of spice mixes like pav bhaji masala, kabab masala, meat masala, chicken masala, cajun spice mix, chipotle seasoning etc.  My personal favourites are Chicken Masala and Cajun spices. 
A common misconception is that chicken and meat masalas cannot be used by vegetarians and vegans, assuming it has meat in it. Chicken and Meat Masalas have the regular ingredients - dry ginger, garlic, onion powder etc. Read the ingredients list on the pack to be sure.

Homemade Ginger Garlic Paste - Equal amounts of ginger (adrak) and garlic (lahsun). Peel the garlic. Wash the ginger and let it dry. Peeling the ginger skin is optional, I don't. Roughly dice ginger and garlic. Grind ginger garlic in a blender/mixer adding oil in small amounts. I generally use olive oil. You can add salt and/or vinegar along with oil as well.
Keep it frozen in a freezer safe container. 20 - 30 minutes is enough to thaw/defrost. Oil works as a preservative, so freezing is not absolutely necessary. Refrigeration also would preserve the paste.
You can make ginger paste and garlic paste separately if you like.

How to cook gravy/sauce for Indian curry - For a white color gravy, use green chillies and/or black pepper powder. For an orange or red gravy, use red chillies which impart a nice red color. I generally use mild dry Byadagi Red Chillies which are quite popular in Karnataka and Maharashtra for its color. Spanish Paprika and Kashmiri Lal Mirch Powder are also mild, but give a nice red color to sauce.
I generally use a mix of two chilli/pepper powders - Cayenne Pepper for heat and Kashmiri Lal for color.
Generally sauteed onions and tomatoes are the main ingredients of a curry sauce. For a white or orange sauce, saute onions just till they turn soft. Browning onions will make the curry turn brown.   
Cashews/Kaju and Almonds/Badam enhance the taste and also help in thickening the gravy. Soaking raw almonds in water overnight is considered very nutritious. I prefer adding the almond skin, as the skin has nutrients too. Make sure you discard the water. These soaked almonds make any curry healthier. Walnuts/Akrot and Almonds are considered low calorie nuts as compared to Cashews.
Fresh or frozen shredded/grated coconut is used in South Indian curries.
Milk or Curds/Yogurt or Sour cream when added to any curry, balances its spiciness and makes the curry creamy.