Make highlighter tools go straight within the text
so that my lines woulnd't go up and down
Laura Chalifoux commented
I accidentally discovered a "secret" trick to getting a straight line with the highlighter pen. It doesn't happen by magic as you're drawing (but then, neither does a highlighter pen on paper). However, you can turn a wobbly highlighter line into a nice straight one, which you can then dupicate, move, change the color, change the line weight, make the line longer or shorter, etc.
All you have to do is select the line you drew with the highlighter tool. On the selection rectangle, pull the top middle square "handle" straight down. You'll see the line get flattened until it's straight.