Using cold water (about 40F) is a must. 
This keeps the batter from becoming sticky. When you add the flour, whisk quickly just to mix it in evenly. Sticky batter results in oily tempura. 
1 egg, beaten
1 cup COLD water
2 tablespoons dry white wine
1 cup flour
Beat the egg and mix with water. Add flour and whisk quickly.
1 tablespoon dashi no moto in 1 cup of water, boiled for two to three minutes
2 tablespoons mirin. 
You can replace this with 1 tablespoon sugar, 2 tablespoons sake or dry white wine, 1/4 cup soy sauce, ginger root to taste, freshly grated (optional).
After you boil the dashi, turn off the heat and add the rest of the ingredients.
[Vegetables & Fish]
Carrots - cut into thin sticks (i.e. 1 1/2 inches long)
Onions - sliced
Green pepper - cut into rings or any way you want
Eggplant - thinly sliced 
Broccoli - prepared as for a for salad
Green onions
Zucchini - thinly sliced
Mushrooms - halved, or whole if small 
Green beans - halved lengthwise or whole Asparagus - bite-sized (deep-fry 3 or 4 sticks together) 
Butternut squash - bite-sized thin slices 
Okra - halved lengthwise
Snow pea pods - whole Cod
bite-sized Shrimp - peeled - whole. 
Dip shrimp in the batter by holding the tail fin, and fry two or three at a time. 
Scallops, whole if small Crab, break shell and expose meat before dipping in batter Squid, sliced into rings or strips 
Dredge fish in flour before dipping in batter. 

Direction:

Heat the oil to 340F or 360F. Dip the vegetables or fish in the batter and place them in the oil. If it is difficult to handle the vegetable chunks, you may use a tablespoon to drop them in. Do not fry too much at a time, in order to maintain the temperature. Take the tempura out of the oil just when the batter gets SLIGHTLY brown. Vegetables usually take less than two to three minutes. Remember: the thinner the vegetable, the faster it cooks. For fish, the time to pull it out is when the batter turns very slightly brown. It is good idea to do trial frying in the beginning. Taste it and decide how long it will have to be fried. Once you get the timing right, the rest is simple.
Serve with tentsuyu. Tempura is also served with rice. This is called ten-don. Put warm rice in a bowl or on a plate and place tempura on top of the rice. Pour on two or three tablespoons of tentsuyu. Another popular way of serving tempura is over a bowl of noodles. This is called tempura-udon or tempura-soba, and it is traditional Japanese fast food.
There are many variations in tempura frying. You can mix two or three vegetables and fry them together. This is called kakiage style. So be creative and invent your own style. 

*** For Details about Ingredients , check your nearest Japanese Store.