If a new tube leaks soon after you put it on the bicycle,  it was probably caused by one of these:  The tire still had a thorn or the piece of glass in it that punched a hole in the old tube, and now it has punched a hole in the new tube - or, the spokes nipples were not covered up by a liner and a nipple punched a hole in the new tube - or, a spoke was sticking up above the nipple and the spoke punched a hole in the new tube - or, the tire came off the rim causing the tube to come out at that place, causing the tube to burst - or, there is powder under the valve causing it to leak - or, you pinched a hole in the tube as you were putting the tube on the rim. 

Before you put on a new tube, feel all inside the tire and see if you can feel a thorn, piece of glass, wire, etc. that is sticking through the tire.  If the object is a piece of wire, you may be able to pull it out with tweezers from the inside of the tire.  You cannot pull out a thorn, piece of glass, or a tack from the inside of a tire because the end of the object that is toward the outside of the tire is larger than the end that is inside the tire.  For objects that you cannot pull out from the inside of the tire, you will have to find the object on the outside of the tire and dig it out with the sharp point of a knife from the outside of the tire - don't stick the knife too far in the tire and don't cut the tire.

After you have removed anything from the tire that could stick a hole in the new tube,  look under the rim liner (don't stretch the liner much because liners can easily break after they get old) to make sure that no spoke is sticking up above the nipple, because if it is, it will punch a hole in your new tube.  The reason that spokes are sometimes sticking up above the nipple is that someone tightened the spoke, maybe months ago, and the spoke had stretched causing it to stick up above the nipple when tightened.  File off the end of the spoke that is sticking up above the nipple.  Check the rim liner to see that it covers the nipples.  Sometimes there will be a hole in the liner at a nipple and the nipple could work through that hole and then make a hole in the new tube eventually.  If the liner has some holes in it, you do not have to throw away the liner - you can cut some pieces of rubber from an old tube and put it under the holes. 

Next,  partly inflate the tube - barely round it out - and put it in the tire.  Then, put  one side of the tire on the rim.  Next, start putting the other side of the tire on the rim while looking to see that the tube does not get pinched between the tire and the rim.  Start putting the second side of the tire on about 8 inches from the valve stem so that the last part of the tire that you put on the rim will be the part that is at the valve stem.  If some of the tube is getting between the tire and the rim as you are putting the second side of the tire on the rim, you can use a tire tool to puch the tube out of the way so it won't get pinched.  You can easily pinch a hole in the tube while you are putting it on if you are not careful.  You will probably need to let some air out of the tube in order to put the last part of the tire on the rim. 

After you have put the tire on the rim,  check to see if the valve stem is straight.  after you get the valve stem straight, push the valve stem up into the tire, then pull it back out until you are sure it is down against the rim. 

After you put the new tire and the tube on the wheel,  don't air up the tire completely because the tire may not be far enough down in the rim in one or two places, or it may be too far down in the rim in some places.  Just put enough air in it so that the tire will stay in place and so that you can pull the tire up if it is down in the rim too far in some places, and so that you can push it farther down in the rim if it is not far enough down in some place.  The tire must have enough air in it so that it will stay where you push it down or pull it up, but not so much air that you cannot push the tire down or pull it up. After you have pushed the tire down in some places and pulled it up in other places, you will need to look all around the tire on both sides to  to make sure that the tire is down in the rim evenly everywhere.  Some new tires, especially wide tires, will blow off the rim when you air them up all the way if one place on the tire was not far enough down in the rim.

Powder under the valve:  With any brand of tubes, sometimes the valve will not seat properly because there is powder under it and air will leak out of the tube at the valve. After you air  up the tire, check to see if the valve is leaking by putting some saliva or some soapy water on the valve to see if it makes a bubble.  If it makes a bubble, air the tire up tight and let several short bursts of air out to blow out the powder that is under the valve core.  Then check the valve again to see if it makes a bubble.  If it makes a bubble again, take a valve core removing tool and see if the valve core is tight, and if it is not tight, tighten it. Then check to see if it leaks. If it still leaks, use the valve tool to take the valve core out of an old bicycle or automobile tube and put it in the new tube.  You may need to clean the valve seat inside the valve stem.  If it still leaks, try another valve core. 

As you air up a tire completely, look all around on both sides to be sure that the tire is not coming off the rim at a place where it is not far enough down in the rim. If the tire is not far enough down in the rim at a certain place, you will need to let enough air out of the tire so that you can push the tire down at that place but don't let so much air out that other places will go down in the rim too far.