There's been plenty written on the subjects of how to tab and highlight the code books. Everyone has their own idea on the subject, most are pretty good. My recommendations are:
Tab the main clause and use an abbreviation for the clause, i.e., 1-Gen, 2-Design, 3-Prequal, 4-Qual, etc. Real estate is at a premium, so don't waste it. Rotate the colors, red, blue, green, etc. for each clause.
Tab the first page of the tables and figures right behind the tab for the clause. Use the same color as the tab for the clause.
Highlight EVERY footnote and write the letter right beside the highlight so you can't miss it. If there is a footnote, that's where the answer is found!
Clause 4 - Qualification; there are several tables for procedure qualification and several for welder qualification. They are easy to mix up when one is in a hurry (can you say EXAM?). Make a BIG letter P in the middle of each table that addresses Procedure Qualification. Make a BIG letter W in the middle of the table that addresses Welder Performance Qualification. Use a yellow highlighter, make the letters big so they cannot be missed.
In each clause that references another clause or table, underline the clause and write the page where it is found in the margin of the code. I call those forwarding addresses.
I prefer underlining using red or green gel pens over highlighters. I find the highlighter too distracting. Only underline key words or phrases. There are only a few instances where it makes sense to underline an entire sentence.
I use "Notes to Self" in the margins to draw my attention to a subject. For example, in clause 5 Fabrication I wrote the note "Fitup" right next to the clause titled "Tolerances". I also wrote a note in the margin where the geometry for a back gouge is addressed and the repair of root openings that are excessive.
In clause 2 Design I wrote notes in the margin for "Design Drawings" and "Shop Drawings" to differentiate what information must be provided by each.
In clause 3 I place paper clips on the pages listing the metric prequalified details so time isn't wasted looking at them by accident.
I placed a paper clip (I should use a tab) for the glossary found in the Annex.
Add key word to the index if they are not already included. Example "F-numbers".
Hope that is helpful.
Best regards - Al