Woah, hey! I'm always happy to talk about my PHB tabs :) Here's a quick breakdown behind my mentality of it and then my execution and some cons of tabbing:

Why?

From a new player's perspective (or someone who likes to loan their PHB to those who are new), the PHB can be pretty daunting to pick up and use as a tool at the table. The sections are huge, and the only way to tell that you're in one section versus another is some very light text on the bottom page corners with some (lacking) color-coding that doesn't correlate to the Contents page -- and the sub-sections aren't given any different kind of treatment so it all kinda blends together. I don't expect most people to read it front-to-back either, so needing to reference something quickly can be difficult if you don't have the muscle-memory down.

Additionally, there are quite a few pieces of information I need to look up with some regularity that aren't part of the Contents and aren't indexed well, so I needed a way to pick them out specifically and quickly with some kind of tactile solution.

How?

So I decided to just tab all of the subsections, then the smaller topics -- the sections themselves are already too large to bother putting an extra tab in for, and I can just use the color-coding in the bottom corner if I manage to get lost. I use vertical Post-It tabs for the subsections, and horizontal Post-it arrow tabs for the topics that match in color to the vertical subsection tabs (not only is it useful, it makes it look beaauuutiful!). It took me a weekend to do, but I didn't have a super well-planned tab structure in mind so there was a lot of redoing that took up extra time.

Pro Tips:

1. Start with the vertical tabs as that'll define where you place your next vertical tab (beneath the first) and your horizontal tabs for that subsection.
   
2. Make sure to get tabs that can be repositioned so if something gets out of place, it's not life or death.
   
   

   My PHB Tab Breakdown
   

   
   

• pg17 - Ancestries & Classes [Light Blue]
  
  • pg19 - Dwarf
    
  • pg21 - Elf
    
  • pg27 - Halfling
    
  • pg29 - Human
    
  • pg33 - Dragonborn
    
  • pg35 - Gnome
    
  • pg39 - Half-Elf
    
  • pg41 - Half-Orc
    
  • pg43 - Tiefling
    
• (No vertical tab for Classes, start horizontal tabs in-line with Ancestries) [Dark Blue]
  
  • pg47 - Barbarian
    
  • pg51 - Bard
    
  • pg57 - Cleric
    
  • pg65 - Druid
    
  • pg71 - Fighter
    
  • pg77 - Monk
    
  • pg83 - Paladin
    
  • pg89 - Ranger
    
  • pg95 - Rogue
    
  • pg99 - Sorcerer
    
  • pg105 - Warlock
    
  • pg113 - Wizard
    
• pg143 - Equipment [Lime-Green]
  
  • pg145 - Armor
    
  • pg147 - Weapons (probably could've been put on pg149 to be more useful)
    
  • pg151 - Kits & Packs
    
  • pg155 - Tools | Mounts (Separate Tabs)
    
  • pg159 - Food, Drink, & Lodging
    
  • pg161 - Trinkets (I never use this, it turns out)
    
• Note: We don't use Feats in our game, so they aren't tabbed.
  
• pg173 - Abilities [Yellow] (No vertical tabs; tbh, never use this section either)
  
• pg181 - Adventuring [Pink]
  
  • pg183 - Movement | Vision
    
  • pg187 - Resting
    
• pg189 - Combat [ Red]
  
  • pg189 - Initiative | Bonus
    
  • pg191 - Reactions
    
  • pg193 - Actions
    
  • pg195 - Attacks
    
  • pg197 - Damage & Healing
    
• pg201 - Spells [Purple]
  
  • pg203 - Concentration
    
  • pg211 - A
    
  • pg217 - B
    
  • pg221 - C
    
  • pg231 - D
    
  • pg237 - E
    
  • pg239 - F
    
  • pg245 - G
    
  • pg249 - H
    
  • pg253 - I
    
  • pg255 - J, K, L (Single Tab)
    
  • pg257 - M
    
  • pg263 - N, O
    
  • pg265 - P
    
  • pg271 - R
    
  • pg272 - S
    
  • pg281 - T
    
  • pg285 - U, V, W
    
  • pg289 - Z
    
• pg291 - Conditions [Light Blue]
  
• Note: Gods and Planes aren't something I constantly need to know about since Matt makes up his own stuff, so I didn't tab this section.
  
• pg305 - Creatures [Lime-Green] (I only tabbed this section since it's useful as a DM when I don't feel like peeling through my DMG or MM)
  
  ---
  
  Obviously each PHB is unique to its owner, and any tabbing will reflect that; in this exercise I've already discovered tabs I never have needed to use, and there are whole sections I omit because it's not commonly needed for the games I play in/run. I do think that having alphabetized spell tabs has been the BIGGEST time saver out of everything, closely followed by the Classes tabs, so you may want to start there -- though that could lead to tabs not lining up nicely, so if aesthetics are important, just plan out your tab structure in advance then go for it!
  
  

  Cons
  

  
  There's only a couple issues I've run into. One is that the tabs that stick out way further still have sticky backs to them and sometimes they get stuck to the other tabs or my arm/sleeves. So far all the tabs have stayed on really well, but it can be a little annoying to peel them off each other.
  
  The other issue is that I have to be really careful with how I store my PHB now; I can't toss it into a drawer or with the tabs facing a surface it'll smash into, since I'm worried it'll mess them up. It's survived like this for at least a year now, so while it's not really inconvenient I just have to keep it in mind.
  
  

  Supplies
  

  
  Vertical subsection tabs: https://www.amazon.com/Post-1-Inch-Yellow-Dispenser-686-ALYR1IN/dp/B00HNW7E84
  
  Horizontal topic tabs: https://www.amazon.com/Post-Colors-47-Dispenser-Dispensers-684-ARR4/dp/B00006RSO4
  
  

  Pictures!
  

  
  
  Edit: Wow, thank you for the gp! No idea what it does but I'll figure it out ♥

First off, this is really an interesting question. Congrats on transferring and best of luck.

OK, so my tips as former adjunct and current instructor doing the Ph.D. thing is this: don't read passively. Don't just sit down, open a book and look at the words. Read actively: sit at a table/desk; have a notebook with a pen out and also invest in a those little tabby flags http://www.amazon.com/Assorted-Bright-Colors-Dispenser-4-Dispensers/dp/B00006RSO4/ref=sr_1_5?s=office-products&ie=UTF8&qid=1453265141&sr=1-5&keywords=post+it+flags

and mark everything that seems significant. Reading literature isn't about regurgitating something you think the professor will find interesting but rather finding your own reading. The best thing to do, of course, is practice: read other things in an active manner. Write up your thoughts and questions in the notebook. This will come in handy in class because there is ALWAYS a moment where a prof asks you to come up with something. Yes, there will be memorization etc to some extent but this is much easier if you're reading actively all along.

Edit: EIGHT years on this site- never been gilded, not once. WHAT DO I DO WITH THIS AMAZING POWER!?

Not OP, but I'm pretty sure those are all Post-it brand flags. Should be at any office supply store or Amazon. These look like the smaller, arrow ones.

​

u/blizter - for you also.

Some wires have gotten crossed somewhere because I have no idea what you're talking about. Yes, post-its. This is the product Anna recommended, it's Post-It branded.
https://www.amazon.com/Post-Colors-47-Dispenser-Dispensers-684-ARR4/dp/B00006RSO4