Whenever you start a project it's good to start with pen and paper because you can quickly iterate and it doesn't take a ton of effort and time to redraw something.
Although you may not want to, you should invest in a $1.75 notebook and not jot on random pieces of paper. The notebook lets you organize your ideas. It can also be something to look back at to see your progress.
If you plan on making a complicated contraption don't go straight to CAD but draw it out in your notebook to simplify it and go through it. then, go onto CAD to design it. this will save you a lot fo time and headache.
When stating parametric for your designs in your notebooks make it as if you were in CAD. When drawing straight lines try to use rulers as much as possible to keep your drawings clean and concise.