What ideas do you have for how to make monster entries in a sourcebook better?
Reduce the stat block. It's wildly oversized. Remove most of the numbers and stats listed. Use that space to include some of the text from older editions that helped with making the monsters more interesting. Like adventure hooks, common goals, tactics, monster roles, lore DCs, number appearing, encounter groups, ecology, etc.
Something like this would more than suffice as the actual statblock.
Gnoll. AC 15. HD 5, hp 22. Attack +4, one per round (bite, spear, or bow). Damage 1d6+2. Move 30 ft. Checks +2/+0/-2. Morale 8.
Rampage. Reduce target to 0 hp, bonus action to move 15 ft and bite.
There's nothing in the full statblock that's necessary to run a gnoll that's not also represented in those two lines. Stats are all +2 to -2, that's the "checks" entry. Pick two stats for each. Should be obvious from the monster. CR is a terrible design. We don't need to waste space on it. Everything has darkvision, especially the monsters. It's not a question of if, rather how far. Almost always 60 ft, 120 ft, or 360 ft. Pick one. Passive perception? It's either 12, 10, or 8. Pick one. Ranges break down to melee, short range, long range. Almost nothing happens at long range in D&D. Listing ranges for the same weapons for every monster in the book is a waste of ink and space. Averaged the damage across the attack types. They're only descriptive differences.
This eliminates redundant information and saves a heap of space...so we can have all the goodies back from older editions I mentioned above.