The amount of lights you will need will depend on the size of your Christmas tree. As a starting point, check it. 6ft tree, now how many lights? For a 6ft tree 240 lights is the basic amount.
If you want it to be more sparkle go for 360 or 420 lights.
You can opt for a wave shape, crossing the lights around the tree from top to bottom; triangle is another option, displaying lights vertically; and branch wrap is also a very popular way to display your lights.