Choose your wood
Check if the wood is straight or slightly bent on all sides
Make a line of where to cut after you know if the wood is straight or not. In my case the wood wasn't straight so I had to make the line in an angle so the wood ends up straight after I cut it.
Make a V mark so that you know where you should cut and also if you end up making a mistake while cutting you can redirect yourself.
Start by sawing the starting point to know where to start from. While you cut check if you're cutting straight every few seconds