Where most people fail is in not knowing how to assess their edge. On that front, I offer these tips:
•Hold the blade edge-up under bright light and look directly into the edge. Do you see any reflective spots? If so, those are dull points. A sharp edge looks like it vanishes into nothing.
•Rest the blade on your thumb under its own weight and rock the blade gently side to side. If it sticks in both directions, that spot is sharp. If it slides one way and sticks in the other, the edge is rolled or has a burr that's folded towards the sticky side. Give a couple of strokes on that spot and test again to see if it trues up the apex. If it slides both ways, it's totally dull in that spot and needs more work. Test several spots down the length of the blade in this way.
•An easy way to find the approximately correct angle to be sharpening at is to just imagine that you're trying to take thin slices off the stone. Instinctually, people usually end up with an appropriately low angle when using this method. The first time you sharpen a knife in this way, you may not be hitting the apex right away. Look at the scratches made by the stone and see if they're hitting the edge or not. If they aren't, keep sharpening at that angle on a coarse stone (so you aren't doing it forever and a day) until the scratches go to the edge. Future touchups will then be a snap. If you need to check your angle, just visually halve a 90° angle to 45°, then again to 22.5°, and so on and so forth. It'll help you identify what angle range you're roughly within.
•When working on building consistency in your stroke, think about locking as many of your joints as you can so you have as few parts of your body pivoting as possible. Use a second hand on the back of the knife blade and turn from the hips and work from the shoulders, not the fingers and wrists.