I think Favored Enemy and Favored Terrain are interesting ideas, but there is one problem: The choice of terrain and enemy is a build choice. If you don't end up fighting that enemy or terrain, it's not so useful. Two options:
Studying certain terrains and enemies grants you generic benefits that don't just apply to that enemy. So, say, a Favored Enemy "Dragon" gives you a bonus to damage against flying enemies. Favored Enemy "Orcs" might give you a bonus to defense against Axe attacks and maybe you know herbs that counter-act the effects of Rage. Favored Terrain Forest means you're good at running through difficult terrain, Favored Terrain Desert means you're resilient to thirst and can withstand fire and cold better. Favored Terrain Underdark might give you low-light vision.
Allow a Ranger to study enemies or terrain to gain benefits.
- Assess Enemy: Take an action to study a foe. That enemy has disdvantage on his next attack against you. Next turn, when you attack, you have advantage on the attack. If you hit, you can knock the enemy prone, disarm him, or push him a few squares.
- Assess Terrain: Take an action to study the terrain. If you move through difficult terrain, mark each square you touched, up to one square per your level. Allies entering those square can ignore the difficult terrain. If an enemy moves adjacent to one of your allies on those marked squares, that ally can use a bonus action to knock it prone. If an enemy moves adjacent to you while you or him is in a marked square, you can use a bonus action to make an attack against him.
- Assess Tactics: When an enemy starts his turn, spend a bonus action to assess tactics. The Ranger figures out what, given the current surroundings, considering obstacles, combat stances and the like, the opponents best promising could be. Denote an area with a Burst 1 where opponents should move to, or one of your allies (or yourself) they should attack. If they don't move into the zone, they grant advantage to attacks until the start of their next turn. If they don't attack that ally, they have disadvantage on their attacks during this turn. If you're in your favored terrain or fighting a favored enemy, you may use this ability a second time before the start of your next turn.
Beyond that:
Expanded uses of Survival - avoid making the Ranger auto-succeed at stuff that turns the whole trip into a non-event, because then the wilderness adventure is over and the Ranger might have been useful, but didn't really get to enjoy some Rangery-Thing-Spotlight.
Finding herbs for potions, poisons, anti-toxines, spices and the like. He might be able to maintain a small supply of healing supplies that rival magical potions in effectiveness, but might lack the shelf life, or are a bit more specialized - he creates a non-magical healing potion that lasts only a few hours before it goes stale and useless, maybe he can create potions to cure a specific disease or poison.
Finding out stuff about the world and environment that would be useful. Maybe he doesn't get to avoid the Goblins or Shadow Beasts sneaking up on the party either, but he instinctively knows more about what kind of threat they pose, where they'll attack.