Before getting all achievements, you should play through the game once. This will help quite a bit when doing the speedrun achievement.

Completing the game once will net you the achievement titled "Beat the Game". To do so, follow all of the narrator's instructions. This will take no more than 20 minutes.

During the first playthrough, more achievements can be unlocked. Unlock the "You Can't Jump" achievement by spamming the spacebar during the game.

Now, pause the game and go to the options menu. Then enable achievements, to unlock the "Achievement" achievement.

"Click On Door 430 Five Times" should also be completed during your first playthrough. Simply click on door 430 five times, then follow the narrator's instructions until you, once again, click on door 430 five times. This is one of the most time-consuming achievements, so it is recommended to be done early on in the game.

Once you reach the office and have to use the keypad, enter '8888' then '8888' instead of the passcode to unlock the "8888888888888888" achievement. Then proceed to enter the correct passcode.

Now complete the game to get the "Beat The Game" achievement.

This will conclude your first playthrough and you now should have half of the achievements.

After beating the game once, close the game. Now go to your settings and set the clock at least 5 years into the future. Then re-open the game. This will reward you with the "Welcome Back" and "Go Outside" achievements. Now you should have 7/10 achievements.
(Or, if you really want to do it legit, actually wait 5 years after closing the game before re-opening to get the "Go Outside" achievement, the earliest date to legitimately get the achievement would be Oct 17, 2018)

Now, play through to the office again, and enter the code on the keypad BEFORE the narrator says the code. Pause and restart. Play back to the office, wait for the door to open, and restart again. Repeat until the door is automatically opened. This is needed for the speedrun achievement.

Now, keep restarting the game until you are in a different starting location. It will be a blue room of sorts. Run through and go to the right around the wall and out the door. Then play the game normally as quickly as you can. It may take a few tries, but in the end you'll get the "Speed Run" achievement.

The other place to spawn would be the speedrun hallway, which is a straight hallway that you will see at spawn. Run straight down the hallway. Then play the game normally as quickly as you can. It may take a few tries, but in the end you'll get the "Speed Run" achievement.

At this point, you should only need the achievements titled "Unachievable" and "Commitment".

The "Unachievable" achievement can be unlocked in one of two ways. One is by getting it randomly, but nobody wants to wait for it. So instead, go to your files in
C:\Program Files (x86)\ Steam\SteamApps\common\The Stanley Parable\thestanleyparable\cfg\
Open the file config.cfg in a text editor (like Notepad++) and on a new line bind a key on the keyboard to “~;_u”. Click on that key in-game to get the achievement.

Now for the final achievement. The way I did it apparantly does not work for everybody, so if it doesn't work you may have to leave your PC running all day. The way I did it was open the game then alt+tab to settings. Now change the date and time to Monday at 11:58p.m (23:58) then alt+tab back to the game. The reason for the 2 minutes is because it is a bit slow loading back up after tabbing over. Now, wait for a few minutes until the computer's clock reads at least 12:01 (00:01). Then alt+tab back to setting and set the time to 11:58p.m (23:58) again (this time on Tuesday) and tab back over to the game. Play a couple minutes, and the "Commitment" achievement should unlock.

Using the clock methods for the 'Go Outside' and 'Commitment' achievements will invalidate them on achievement tracking sites, such as Astats. It's your choice to do them legit or not, but I am not responsible for any bans/invalidations.