I decided to make this short guide since P4G is notorious for not giving new players enough info to figure out how to get to the Golden Ending and see every Golden-exclusive piece of content by yourself. If you follow it you will get the most out of your first playthrough without reading walls of text or following a strict day-by-day walkthrough religiously.

Prioritize those S. Links. Marie unlocks a new dungeon and the Golden Ending and Adachi adds a lot of new scenes later on in the story. His S. Link progresses automatically after you get it to Rank 6 so don't worry about it. You don't have to romance Marie, whether you do or not changes nothing, so decide on your own.

If you really don't like Marie then you can ignore her completely and still get the original PS2 True Ending of the game. The extra dungeon and the winter segment will be skipped completely this way. This is not recommended since this content is pretty enjoyable (and is considered canon judging by the spin-offs). You will still see all of the Adachi scenes this way.

If you still want to avoid the extra dungeon and winter segment after maxing Marie's S. Link for some reason, tell Margaret that you want to forget about Marie when prompted by her in January. You will also get the True (not Golden) Ending this way. This is obviously not recommended as well.

Don't read this until you clear the Heaven dungeon (this is pretty late in the game). I'll try to make it as spoiler-free as possible:

On 12/03 choose the following responces when prompted by Yosuke:
1. Wait a second here...
2. We're missing something.
3. Namatame's true feelings.
4. Something's been bothering me.
5. We're missing something...
6. Calm the hell down!

On 12/05 choose the correct person.
If you decide to protect this person if asked, you will instead get another Golden-exclusive Accomplice Ending. This is on of the "bad" ends, so if you decide to go for it make sure to make a save file before this point so you can continue on later. This ending is still worth a view so it won't hurt to see it at some point.
Keep in mind that if you choose an incorrect person you will just get a regular Bad End, so have a save file ready either way.

On 03/20 talk to all of your maxed S. Links. After the game asks you if you want to go home, select "No" and go to the Junes Food Court instead.

Whether you get Golden or True ending is decided by if you have maxed Marie's S. Link or not.