The Golf Club

The other guide is great for the party planner achievement but I didn't find it too helpful for this achievement due to the fact that at least one of your new found friends either have to
a) accept your invite, or
b) be playing the same course as you when you send out your invites

Neither of which was the case when I popped the party planner achievement, they'd all moved on to other courses and ignored my invites.

So if you don't earn this while earning party planner my recommendation is to add friends as per the other guide but rather than send out invites, select join game on an active friend. Finish the round and the achievement should pop.

This achievement is not hard to achieve i personally got it while going for the "Party planner achievement".

To complete this achievement you just have to complete a round of golf while there is another person on the same course as you.

The following is how to find people who you can join your game. I found it better you use a official course as there is more people playing on them. I used
Little Brook Manor as it is one of the most active courses.

(Credit to the following-The Globalizer)
* First, start a round of golf.
* To find some "friends", select "Change Rivals", then "Global Recent". This will give you a list of people who have recently completed a round.
* Press cn_X to bring up the gamercard of the selected player. If they are still in-game, add them as a friend. (They don't need to accept your friend request.)
* IMPORTANT: Dashboard (press cn_guide) and close out the game. To do this, press the menu cn_start button on the game, and select "Close".
* Reload the game. This will refresh your friend list in-game.
* Start another round of golf.
* Pause and select "Active Players". This should give you a list of players you just friended.
* Press cn_A on each and select invite. (They don't need to accept the invite.)

-If you have any questions or improvments just leave a comment below

(edit-10-5-2015) the achievement will pop on completion of the WHOLE course.