Fibonacci retracements inherit every error baked into the swing you choose. If the high or low is cosmetic rather than structural, the entire grid drifts.
Start with swings that changed the character of the move: a break of structure, a session extreme that attracted genuine follow-through, or a pivot that later became support or resistance. Ignore wicks that never attracted a second attempt.
On lower timeframes, confirm the same swing on one higher frame before you commit ink to the chart. When the anchors disagree, the higher frame usually wins.
Finally, write the reason for each anchor in one sentence. If you cannot explain why that high or low mattered, erase the level and start again.