Most trees have a natural direction of fall. This is affected by the tree’s lean, the shape of the branches and crown snow-load or snow-covered branches. If you are unsure of the tree lean, move away a little and check with a plumb line.
To some extent, you can force a tree to fall against its natural falling direction, but this requires knowledge, experience and the right felling support tools. Trees with weak timber, such as dead or decayed trees, should always be felled in the easiest direction.
Finally, handling the saw. There are a few techniques that will make your work safer as well as easier.