I've been thinking on this lately, and propose the following:
Skills
Skills are important to characters as they help to define what a given individual is capable or incapable of performing.
Non-Proficient A character who is non-proficient in a skill adds one-half their ability score modifier to the roll. If you have a negative ability modifier, you subtract the full ability score modifier from the total.
Proficient Characters who are proficient in a skill add their proficiency bonus and their full ability score modifier to the total.
Expertise When you gain expertise in a skill, chose a subskill from the appropriate list for each skill. When you perform skill checks involving the subskill you add your ability modifier and twice your proficiency bonus to the result. You otherwise act as you have proficiency with the skill, allowing you to add your proficiency bonus and ability score modifier to the total. If you have a negtive ability modifier, you instead treat it as 0 when you use the skill.
Mastery If you have mastery of a skill, you gain the benefits of expertise with the skill. Also, once per short rest you can choose to automatically succeed on a skill test with the skill. Furthermore, if you are not rushed or under pressure, you can choose to change the result of the d20 roll to equal 10.
Listed below is a list of skills according to the ability they are normally associated with. A list of expertise subskills is listed for each skill.
Strength
Athletics. Climbing, Jumping, Lifting
Dexterity
Acrobatics. Balance, Escape, Tumble
Sleight of Hand. Conceal, Palm, Trickery
Stealth. Hide, Silence, Surprise
Constitution
Endurance. Fortitude, Resistance, Revival
Intelligence
Arcana. Aberrations, Alchemy, Existential (Planar Group), Spellcraft, Traditions (Specific)
History. Ancient, Legendary, Monstrosities, Recent, Regional (Specific)
Investigation. Deduction, Factfinding, Interrogation
Religion. Afterlife, Celestials, Fiends, Rituals, Spellcraft, Traditions (Specific)
Nature. Beasts, Fey, Plants, Terrain (Specific), Seasons, Weather
Wisdom
Animal Handling. Command, Husbandry, Ride, Train
Insight. Empathy, Familiarity, Humanoids
Medicine. Diagnose, Herbalism, Stabilize, Treatment
Perception. Listen, Smell, Spot, Taste
Survival. Camping, Hunting, Tracking, Trailblazing
Charisma
Deception. Cheat, Disguise, Gamble, Fast-talk, Lie, Misdirect
Intimidation. Blackmail, Bully, Insinuate, Violence
Performance. Act, Dance, Orate, Play Musical Instrument (Specific Group), Sing
Persuasion. Bargain, Command, Persuade