Identify what psyllium is doing in your recipe: gel/thickening (binds + holds moisture) vs just boosting fiber/body.
Use the listed ratio from the table; measure by weight if your recipe is weight-based.
If your substitute is seed-based (chia or flax), bloom it first in the recipe’s liquid for 5–10 minutes until thick.
If your substitute is gum-based (guar or xanthan), whisk it into dry ingredients, then mix thoroughly to fully hydrate.
Check batter consistency: if it’s too thick, loosen with 1–2 teaspoons water; if too loose, add a small pinch more.