Hit Dice: d10 puts you ahead of every class except Barbarian.
Weapon Proficiencies: Martial weapons ensure you’ve got options for any combat situation, regardless of your chosen fighting style.
Armor Proficiencies: The choice of light or medium armor means you can have multiple sets of gear for different situations. Light armor for stealth and ranged combat, Medium armor for melee brawling.
Tool Proficiencies: None. Which means you’re limited to your race or background choices.
Saving Throws: Strength saves rarely come into play, but Dexterity saves are quite common. Consider picking up a feat to get proficiency in either Constitution or Wisdom saves to round out your defenses.
Favored Enemy: This basic Ranger ability is very situational. Ask your DM if any one type of foe is going to be featured more often than normal in your campaign to gain the most use out of it. The options are wide ranging, but the most generally useful ones tend to be fiends or undead if your party is mostly of good alignment, and you’re playing a classic heroic campaign. Humanoids is always a good choice, as you get two subrace choices, covering more ground.
Natural Explorer: The bonuses granted are fairly inconsequential if your DM glosses over travel. If you spend a lot of time exploring the wilderness with milieu rolls for survival and random encounters, your party will be glad to have you along. Choose your terrain carefully based on the setting of your campaign.
Fighting Style: You don’t have access to all the fighting styles that Fighters do, but the ones available to you are very useful. This will be the main ability that dictates your build, so make sure to synergize your gear and ability scores with your choice here.
Archery: The obvious and arguably best choice. This synergizes best with your skills and a high-AC, light armor, Dexterity build.
Defense: The AC boost is great for a melee character, but since Rangers don’t get Great Weapon Fighting as a combat style, they suffer from their lack of powerful melee damage output.
Dueling: Don’t forget that this style allows you to hold a shield in your off hand. the 2 bonus damage closes the gap between a single longsword attack and two short sword attacks. This also keeps your bonus action free for spellcasting or other abilties you may have picked up from your ace or other classes.
Two-Weapon Fighting: This fighting style gives you a powerful option in a bonus action. Adding your ability modifier to the damage of your off-hand attack makes your damage output that much higher and makes you a more consistent combat asset. Combine this with the bonus damage from Hunter’s Mark and you become a beast in melee, dishing out massive damage to your opponents.
Spellcasting: Rangers have a very interesting spell list, providing them with a mix of support, enhancement, and battlefield control spells.
Primeval Awareness: A very situational ability that can be mimicked with a very high survival or investigation check.
Extra Attack: As discussed above, Hunter’s Mark and your Combat Style give you solid damage output. Adding another attack to the mix gives you even more usefulness in a fight.
Land’s Stride: If you’re a melee build, getting over the speed bump of difficult terrain is a godsend.
Hide in Plain Sight: Very effective for hiding in place.
Vanish: While not compatible with Hide in Plain Sight, it still gives you a great advantage you can use to snipe targets.
Feral Sense: Invisibility is dangerously overpowered in 5e. Overcoming this is great, especially since you rely completely on weapon attacks and lack and area effect spells.
Foe Slayer: The bonus to attack can be as much as +5 if you’ve taken care to increase your Wisdom along the way. This gives you great consistency in combat.