I use everything, even the needles, but they tend to burn off at once.
The juniper I can find is not really trees, more like bushes. Because the growth conditions, they grow very slow, so the branches are quite thin. I usually use a small saw as well as a set of pliers ment to cut down thin branches on garden trees, like apple, when I harvest what I need in the mountains. A couple of branches from a bush, and a couple more from the next one, so I don't damage them too much.
Beware, this is a evergreen tree with resins, and not really suited for smoking if you are going by "the book". Even so, we have used it for smoking food here in Scandinavia for decades.
Start with a small amount, and increase until you find the taste that you like.
The flavour is quite strong, but is very nice with fish and also with bacon.