The online world of San Andreas has a plethora of things you can do besides missions, deathmatches, and races; and these other, random activites are the types of things that are needed to earn this particular achievement. Disregard the achievement description; it's really not as hard as it sounds.
You can check your progress towards these activities by following these steps: PAUSE > STATS > UNLOCKS > PROGRESS.
There are a lot more activities listed in that menu, but the list below are the ones that are required for the achievement. Next to each activity in the menu, you will notice there will be a "no" or "yes" indicating if you have:
A. participated in that activity
AND / OR
B. completed that activity.
There is no distinction between the two in this menu.
It is possible to participate in an activity required for the achievement and not complete it (due to being kicked, quitting early, cloud server issues, etc.) Your menu will say "yes" but it may not count towards the achievement. Make sure you fully complete the activity. (once you reach the choice menu for your next job, it will count.)
-Get a haircut
-Get a tattoo (cheapest I found was the Scorpion on the right leg for $2400)
-Buy an article of clothing
-Play golf (CAN BE DONE SOLO)
-Play tennis (2 players) (win or lose)
-Play darts (CAN BE DONE SOLO)
-Play an arm wrestling match (2 players) (win or lose)
-Hold up one store (YOU MUST ESCAPE THE COPS FOR THIS TO COUNT!)
-Buy a private dance at a strip club
-Complete any one challenge at an Ammu-Nation gun range (CAN BE DONE SOLO) (win or lose)
-Golf games can be set to one hole. Easiest done with a boosting partner, and if you win you'll get a solid RP Boost. It's not a bad way to grind RP if you get bored of Violent Duct or the prison race!
-Tennis games can be set to one set, although you will need to win 6 games to win the set. This one is probably the most time consuming of the bunch, and this will be the one that a boosting partner comes in handy.
-Holding up stores is easiest done with a friend or two, and will help you work towards the Stick Up Kid achievement. You will get at least a 3 star wanted level for holding up a store, and I've found the cops in GTA Online to be far more pesky than they are in the story mode. Enlist one of your friends as a getaway driver to make it easier for yourselves.
-Many of these minigames count towards the Decorated achievement for winning 30 platinum awards. These include winning a 5 set tennis game, winning a tennis game in straight sets, getting a hole in one in golf, and getting a 6 dart checkout in darts. You can check your progress towards these awards by following these steps: PAUSE > STATS > AWARDS
-Golf, tennis, darts, arm wrestling, and the gun range challenge also count towards the Numero Uno achievement, but please note that you must WIN the game for it to count! If you simply complete the activity without winning, you will need to redo it for Numero Uno, so if you want to save some time on that, boost these activities with a partner.
-Be aware that darts, arm wrestling, the strip club, tennis, and golf do not unlock until rank 7.
If you have any questions or a way to improve this solution, please leave a comment :)