Find the dummy, Kill it, advance to the next room and find a Froggit, Kill it too!
Get to the next room, After the room where you get a cell phone is the best room for grinding, Kill everything until you get the message "But nobody came"
Then fight Toriel, you should kill her in one hit. Then advance

Find sans, you should not go behind the lamp. Papyrus will come through.
Now advance to the room with the box, get the Tough Glove and move on to the room at the bridge with the "Gauntlet of terror" as papyrus calls it, After he exits, talk to sans and he should disappear in a flash of darkness.
Grind every monster in this room, then advance to Snowdin Town where you can get infinite Bisicles and Cinnamon Buns, Fight papyrus and kill him in one hit.

Go to the room after your first Monster Kid encounter and that is the best room for grinding, Kill everything and move on, Shyren counts, Then fight and kill Undyne.

Find mettaton for the first time, Exit the lab and find the next SAVE Point, That is the best room for grinding, Now move on to the Muffet fight, Kill her.
Then get to the CORE and kill everything you find, if you find anything.
Kill mettaton NEO.

Go through the new home, get the keys, and get through all of Flowey's useless dialogue and get to the Last Corridor, Fight sans, Kill sans, Kill Asgore, Kill Flowey, Erase the world.

The only way is after erasing the world, Opening the game and leaving it open for ten minutes and then sell your soul.
Close the game.
Then you have to open Run, (Windows key + R, not sure about Mac/Linux or whatever)
Type in %localappdata%
Open the folder named "UNDERTALE"
Delete system_information_963 and system_information_962
And BOOM! The effects are reset and you beat the genocide run. Congrats.

Thanks for reviewing this guide if it helped you Make sure to leave a like or comment,
This IS My first guide for Undertale so it might not be super long as expected, But that's all!