There are many ways to get good lines or stripes and size is often the deciding factor on which is better.
For larger lines or stripes (say a Racing Stripe down the middle of the Jetbike) I would suggest "painters Blue masking tape" which you can get in 1/4 inch size, has some flexibility to it, and won't leave any residue behind. Another good thing to use is "Blue Tac" if you want to have a stripe that has a few bends in it and you don't mind wasting a little (dollar store) blue tac. You can also go to your local hobby store (check the air brush section) as there are some great "sticky sheets" that you can cut to any size you like and use for taping.
Painting lines can be done in a lot of different ways; but since you mentioned Saim-Hann here is what I would do.
Prime the Jetbike. (Black if yo like the dark look, white if you want your stripes a light colour.)
Tape your lines.
Paint all of your Reds ontot he Jetbike, do everything, shading and highlighting.
Pull the tape.
Highlight your Black stripes or shade your white stripes.
For thin lines or stripes I suggest doing them freehand, and before you say you can't paint that well hear me out. If you paint the Jetbike with all of your reds (do the whole bike) and then just paint over the reds to get your Stirpes... Black stripes go on easy with a standard brush and then just add highlights, and White can be done by doing a layer of Bleach Bone, then a layer White, and then highlight with white as there will be some shadow showing through the first layer of white. It is not that difficult if you take your time.
I hope that helps you out.
Cheers and happy Gaming.
