Take a bamboo rolling mat and place a nori sheet lengthwise on it.
Make sure that the shiny side is facing down.
Also, the sheet should leave out 1-inch of the bamboo sheet exposed from the edge close to you and some part of the mat should be exposed on the other end as well.
Wet your hand with some cool water and place a handful of sushi rice in the center of the nori sheet.
With the help of your hands, spread the rice evenly over the nori.
3/4th inch strip of the sheet however should remain untouched by the rice.
Place the tuna strips, cucumber, avocado and carrots along the center of the rice.
Do not stuff the nori with too much quantity.
With a gentle press from your fingertips on the fillings, they will be held in place.
Using your thumbs, lift the bamboo mat edge close to you.
Start rolling the mat gently and slowly, pressing the fillings as you go.
Keep rolling till it covers the rice and both ends come together keeping the untouched 3/4-inch nori exposed.
Holding the bamboo mat, apply pressure on the fillings to keep the roll firm.
Then slice the roll in half.
Cut both rolls in two pieces so that you now have 6 rolls.
Repeat with salmon and other fillings.
To make the sushi rice, rinse the rice in cold water and remove dirt if any.
Drain the rice.
Take a saucepan and add the rice with 6 cups of water and put a tight fitting lid on it.
Bring the water to boil on medium heat.
Let the water boil for about three minutes and then cook the rice for 15 minutes on reduced heat.
Once the water dries out, remove the rice from heat and spread it evenly on a greased cookie sheet.
Sprinkle salt, sugar, vinegar on the rice and keep mixing till the rice cools down to body temperature.
Cover the rice with damp paper towels till ready to be used.