Levelling skills in the early game

In Kingdom Come: Deliverance, your skills are improved when you use them. Here are several ways to level up key skills during the early game. 

Attributes 

Strength, Agility	Fight using strength-based and agility-based weapons. Learn Leg Day and pick herbs to improve Strength in risk-free conditions.
Vitality	Stand still and jump in place or go next to a fence, hit jump to vault over it, and repeat. Vitality also increases with "surviving combat", so killing animals (even domesticated ones like dogs, sheep, and cows) is a remarkably quick way to level it.
Speech	Talk to everyone. Any topic that is not grayed out will give speech XP. Empty babbling is the most rewarding: e.g. when dealing with multiple options during a quest conversations, don't go for the immediate solution. Instead, offer the money, then change your mind, then say "I'll come back later" and so on. Try all the options that you can back out from before picking the option that is an actual solution.

Combat Skills 

Unarmed	West of Miller Peshek, whom you meet after your return to Skalitz , is a tanner. Find an isolated person in  this area, knock them out, and carry them to the river (taking care not to be seen.) Wade in far enough so that your head is just above water level. Drop the body and proceed to punch it relentlessly until you reach the desired level. The townsperson will stay unconscious, not die, and if done unnoticed your reputation will not be affected.
Defence, Axe, Polearms  and Sword	Early in the main questline you will unlock training with Sir Bernard just northeast of Rattay . Use practice weapons, as their low damage allows you to train longer. Another option is to begin combo training and simply refrain from doing combos in order to extend the session. A third faster-but-illegal option is to kill sheep during the prologue in Skalitz (after herding them into the barn behind Kunesh's house, so they respawn upon returning to the pasture, and so no-one can see the killings), but it will not increase defense because the sheep do not fight back.
Bow	Archery is challenging while your stats are low. Make sure you are using a bow appropriate for your stats or it will be more difficult. During the quest "The Prey," you will be shown a hunting area north of Neuhof and southeast of Talmberg. This area includes deer hunting and tons of rabbits. Killing them with a bow will help you level bow and hunting simultaneously. The easiest way to get there is by heading northeast from the fast travel point for the northern coal burners' camp. Alternately, play Chumps (shooting logs floating down the river) in Ledetchko by speaking to Vatzek. He is northwest of the Miller, on the the northwest side of the large fields across the river. Note that there is currently no penalty (as of 1.2.5) for shooting the logs from in the water, and that archery XP isn't calculated until the match is finished.

Non-combat Skills 

Alchemy	Brew Digestion potion, Poison, Bowman's Brew or Marigold decoction by simply putting all the components into the cauldron and bottling the brew up.
Drinking	Get hammered at your local tavern, sleep it off, repeat. Alternatively, a combination of Digestion potion, Hair o' the Dog potion and any alcohol (e.g. Moonshine potion) allows you to level up this skill very quickly and as high as you want it to be. The easiest way to level up this skill slowly, but steadily, is to have a drink just before you go to bed every evening. This way you won't have to deal with the effect of drunkeness as you conveniently sleep it off.
Hunting	Kill endlessly respawning sheep and cows in Skalitz (prologue) and search their corpses (which counts as gutting - a part of hunting), but make sure that no-one's watching. Kill and gut any animals after the prologue. The best way to level hunting early on is to hunt in the area that you visit during The Prey. Gamekeepers usually don't show up there and you can also get an early boost to bow skills, agility and vitality.
Herbalism	Across the river, north of the miller in Rattay, is large fields with tons of flowers and herbs. Simply roam these fields picking to your hearts content. Similar fields also exist along the road between Rattay and Neuhof.
Horsemanship	Find a nice long road and hold down the gallop button. Pathfinding will keep you on the road. Maybe find some tape to help out.
Houndmaster	Keep telling Mutt he's a good boy ad nauseam. Or feed him a ton of food. Both options never stop giving XP and do not have a cooldown.
Lockpicking	Make sure you start with very easy locks and move up incrementally as you level. Lockpick the doors to homes at night, whistle to get the occupants' attention, then wait for them to go back inside and relock the door. Repeat. You can also simply lockpick the outside doors of buildings in a town, and move on to lockpick the doors of adjacent buildings before anyone investigates (preferably late at night to minimize witnesses). To pick the hardest locks quickly, use the "Luck of the Drunk" perk at lockpicking level 6, which will let you pick any lock in the game as long as the drunkenness status effect is active.
Maintenance	Learn the initial repair skill from the armorer in Rattay. Pick up worn-out swords and/or axes from bandits, and sharpen them at a grindstone. Sparks mean you are doing it right, smoke means you are not. You purposely cause smoke while sharpening to damage the blade, exit the minigame, and then sharpen properly for XP.
Pickpocketing	Possibly the most annoying one. The safest way to raise it is to repeatedly ask Peshek to teach you the skill and getting the experience from his tutorial. Otherwise use savior schnapps before each attempt, have the infamous perk, or just be OK with reputation problems. The best way is to pickpocket drunks, sleeping people, and random isolated people on the roads of the countryside.  There is however a slightly "cheaty" way of levelling up pickpocketing. If you rent the room in the Inn of Uzhitz you will have the gambler as a room mate. Wait until midnight and he will go to bed. Knock him out and loot him. He usually has about 800 groschen on him, so you'll have more than enough money for the fine if you get caught. Now loot him again, but this time put a really expensive item (plate armour) in his invetory and wait crouched near your bed for one hour. The gambler will wake up, go downstairs, come back up again and go back to sleep. You can now pickpocket the expensive item from him for a hefty amount of XP. If you feel like save scumming or just brave, you can put more than one expensive item in his inventory and steal them all back one by one.
Reading	After you have found the scribe in Uzhitz (or chosen the "Scholar" perk to unlock the reading skill without him), buy books from him and  sit down on a bed you own. Go to your inventory and read the books to increase this skill. It is unclear if you are awarded XP for reading books you have already read. Studying books gives more XP. Reading XP can be gained by reading potion recipes, lore books, skill books and treasure maps. Reading all the books you can buy or steal from the Uzhitz scribe are enough to get you to about level 9 reading. Lore books are especially handy, as they don't actually need to be read. Just leafing through them will pay out 30 XP.
Stealth	When you find isolated wanderers in the countryside, sneak up behind them and knock them out.