A trick to make long shots easier is to make them longer! First thing, if the shot is tough, settle for whatever shape you can get by working up and down the centerline of the cue ball and speed. Don't make a tough shot tougher by adding unnecessary factors. With planning it is almost always possible to either have a tough shot or tough shape but not both on the same shot.
If you are dealing with a tough shot with tough shape the percentages have probably dropped below that of making a safety. A personal rule of thumb, I fudge the rule of if the safety is easier than the shot play the safety. I go with if I estimate that the shot is fifteen percent tougher than the safety, play the safety. If I think the safety is almost as tough as the shot, play the shot and keep control of the table.
Back to my opening statement: Particularly long straight shots but it works with cut shots too. Find a spot on the rail or even wall behind the object ball that will cause the cue ball to hit the object ball at the proper angle. Focus on that more distant spot, ignoring the object ball. The object ball you are barely aware of goes in. By aiming at the more distant location you are bringing into play the old rifle shooters' adage, "aim small, miss small."
Hu