I am making a fondant covered cake and the bride wants horizontal stripes to mimic the satin banding on her dress. It will be white on white and thought I could either paint stripes with super lustre or cut fondant ribbons and place them on the sides. Any tips on keeping my lines straight would be a big help.

Hi SRC_Dee,
When ever i have made stripes i roll my medium to what thickness i require - then with a metal ruler and small scapel i cut my stripes.
I leave them sit for about 3 -4 minutes after cutting to let them firm up a bit.
No reason why you can't let them sit a few minutes longer if you wish.
Then i roll them up like a bandage and beginning at the base of the cake - move around slowly unwinding.

If you need to have a space inbetween each stripe - just lightly score the cake surface with a toothpick or point of the scapel and do the same as with the first stripe.

Letting the stripes sit tho after cutting is the best way to ensure that your stripes stay firm and in shape.
Hope this helps you

Forgot to say - i brush where my stripes are going to go with sugarglue just before applying them...and i usually wait about 10 minutes before doing the next one so as not to nudge the first one and cause it too shift.

Bluehue

What about using a laser leveler so that you can see where to place the stripes on the cake.