Amateur designs look 'off' even when you can't put your finger on why. 90% of the time, the culprit is poor alignment. The grid is the skeleton of your design.

The 8pt Grid System

Never use random numbers for spacing (like 13px or 27px). Base everything on multiples of 8. Your margins should be 16px, 24px, 32px, 64px. This mathematical consistency creates rhythm and harmony that the human eye loves.

Optical vs Mathematical Alignment

Sometimes, the computer lies to you. If you mathematically center a 'Play' button triangle inside a circle, it will look too far to the left because the left side of the triangle has more visual mass. You must manually nudge it to the right for optical alignment.

Conclusion

Trust the grid, but trust your eyes more. Master mathematical alignment first, then learn when to break it for optical perfection.