SJX426,
On the vertical ones on the down tube...always the most difficult to do.
1. First measure the length of the decal
2. Cut the decal from the sheet leaving the paper on...leave enough space at the top and bottom so that you can handle the decal without leaving fingerprints when later positioning it.
3. Place the decal with paper backing on the tube and mark a centerline on both the decal and the tube, you can use a dot no need to draw a line....I use a wax pencil, again you only need a small mark to center the decal on the tube.
4. Carefully peel the decal from top to bottom (the extra space left on the edges will facilitate the placement)
5. Start at the top by lining up the centerline dots....position the decal and eye up with the bottom line and you are good to go.

Do a dry run with the paper left on in order to get the feel of it, the directions make it seem more difficult than it is.
Good Luck, Ben
Looks like you have another way to do it posted while I was typing...see which you prefer, not that difficult it will work out