When you reach the part of the game with the bear at the beginning, instead of exiting the area, sneak up to Ralof or Hadvar (depending on your choice) and use a dagger or other one-handed weapon to perform sneak attacks.

Continue to sneak attack Ralof or Hadvar repeatedly to level up your sneak skill. Each successful sneak attack will increase your sneak skill.

You can do this for about 20 minutes to reach 100 sneak skill or take as much time as you need throughout the day. It's entirely up to you how quickly you want to max out your sneak skill.

Be cautious not to lower Ralof's or Hadvar's health too much, as it may have consequences for the game's storyline. Their health will gradually regenerate, so you can take breaks between attacks to avoid accidentally causing their death.

This method can be a fun way to start the game with high sneak skill, allowing you to be more stealthy and effective in your adventures in Skyrim.

and GG