Find or create a table of equivalents and stick to it consistently. Test, re-test, and proofread.
I've written two more since and, though I love the work, the unglamorous truth is the hours are appalling. You may just include metric measures, or you may decide to include imperial, American or Australian measures as well. Thankfully, there is a wealth of book marketing knowledge that authors can tap into when formulating their plan.
However, if you take snaps of your recipes as you test them, that can be really useful in planning the book.
Do you have something extra to offer? In the best case, recipe headnotes will reflect the unique voice of the writer and the tone of the cookbook, and engage the reader with a bit of the recipe's history or lore; a bit more about a particular ingredient or an additional recipe tip or variation; or even a personal anecdote that relates to the recipe in some way shape or form.
This is just a general overview and there are lots more to consider if you want to write a cookbook.