The number one hint is this: rolling sushi is a self-correcting process. If your first roll does not turn right? eat it to hide the evidence and roll another. If it has been a while since you made a roll, keep practicing and it will all come back to you, like riding a bicycle. Once you learn it you can never forget it.
Rice does not stick to nori, or roll does not stick together when rolled. Most likely you did not use enough vinegar in your rice. The rice should be annoyingly sticky.
Roll is too thick, or or does not hold together. You probably used too much rice, or packed it down too tightly. The rice should be spread on the nori to within about 5/8-inch of what will be the outer edge. Rice should not be squished onto the nori, and should not cover the nori completely. You should be able to see nori between the rice kernels, perhaps 1/4 to 1/3 of the space should be open to the nori below the rice.
Cucumber can be cut into larger chunks which are easier to work with. Try quartering the cuke lengthwise, removing the seeds< then cutting the flesh into large pieces about 1/4-inch thick by 3/8-inch wide. The length of the pieces should be half the width of the nori.
Place a square of plastic wrap on or between the nori and the bamboo mat when making rolls. This will keep the rice and messy ingredients out of the mat and make it last longer. Peel the plastic wrap back with the mat as you roll. When you are finished, wrap the roll in the plastic wrap and put the roll in the refrigerator. When you are ready to serve, unwrap and slice them.