Tips and Tricks
If you want to start over, just tap the screen.
Consider the start and finish of your sketch, they're important for motion.
Want to try an earlier level? There's a back button in the bottom left corner.
You lose if you draw a line that exits from the top or bottom of the screen, so it's important to avoid that when possible.
The left and right horizontal edges are a different matter, an in fact you can use them as part of your strategy. Since a line will generally keep going until it exits along the top or bottom of the screen (or runs into a colored dot), you can let it rebound from the edge of the screen and it could keep going to help you solve the puzzle.
If you quickly draw a perfect circle, you will create a portal. You can create multiple portals, then send a line through one. It will emerge from the other, which you can use to your advantage on some of the trickier puzzles. If you decide that a portal is just in the way, tap it to remove it.