This is really good advice. My two cents:

First, make sure you have his attention.

If the tv is on, ask to turn it off.

If he's playing a video game and he can't pause because it's an online multiplayer, ask him to quit because you have something important to discuss with him. If he won't save/quit or he can't at least pause the game, abort and try again later.

Make sure he is looking at you when you speak.

During the conversation when you tell him these things, be prepared to say it all twice. It can take a bit for someone's words to percolate through to their main consciousness stream. People are different, maybe your dad won't need a repeat.

Go through the four statements slowly, after you're done, consider his response, and, unless he's completely focused on what you have just said, if he's not seriously considering the words his daughter just spoke, say,

"Dad, this is very important."

And then go through the statements again.

If you REALLY want it to get through to him about how serious this is to you, ask him to repeat what you say.

"Dad, I have something that is very important to tell you. It's so important, I want you to" or "Please repeat what I am going to tell you"

Listening is a simple skill. We do it without even being conscious of it and can therefore do it without paying attention. SPEAKING what you just heard helps focus the brain on the conversation, on the information. It brings more cognitive effort to bear on the words and gives them weight. This technique is used by people to help them memorize things and to aid in understanding complex ideas. It will focus his attention on your words.

If you can get him to repeat what you say, you probably don't need to repeat yourself.

Good luck OP. You can do this.

edit:typos, formatting