If you are cutting plywood, you will need to provide support for the whole board to avoid splinters and tears. However, when cutting other wood, allow the cutoffs to fall freely. If you have supported both sides then it will bow in the middle and cause the saw to buck and the wood to splinter.
Cutting with the grain of the wood is much easier and gives a neater finish. But when you need to cut against the grain, called a rip cut, extra care needs to be taken. Try fixing the wood down, or using a table saw, to get cleaner edges.
When you need to be really accurate, line the saw up and cut slightly to mark and check where the blade will cut before fully committing.
Once you’ve started cutting, keep your eyes on the markings slightly ahead of the blade, rather than watching the blade itself.
Cutting a straight line takes patience and practise. If you have veered off course, it is easier to cut the power and line the saw back up before starting again, rather than trying to direct the saw back to your markers. – by Roberto Russo