Keep it short, professional, succinct and very readable (e.g. use clear headings to structure), whether or not you have a tight or generous space allowance. Your English must be perfect. Remember that your meta reviewer has a huge caseload and is sick unto death of reading reviews and completely out of time.

1) Thank the reviewers for their time, and state your appreciation that the reviewers found value in X,Y,Z (this should include the things we ourselves feel are most important about this paper which the reviewers recognized).

2) List the top ~3 (or less, as needed) issues that the reviewers had important negatives or suggestions about, then address each of them in turn. Rephrase the question, explain why we did it as we did, and state how we will fix the problem in the scope of a revision, given the limits of space and time before a final submission is due.

3) In closing, you can very briefly deal with anything else - just say that the reviewers also made very helpful suggestions about x,y,z and we will be handling those within the page limits of the paper.

4) If room: thank the reviewers for any suggestions made about additional work, but do not imply that they will be addressed in this revision (in general is not a possibility).