Fall Guys

As of Season 2, linking your Amazon account doesn't help much (you get an Upper uncommon piece aka Rubber Ducky Cap) so I am going to recommend three ways to get this, but first a few tips:

Tip #1: You will want to check the store (fifth icon at the top of the main menu aka the cart) daily to see if they sell any uncommon items in exchange for Kudos (the game's reward currency for playing the game, winning challenges, ranking up, etc.).

Tip #2: When playing, try to win as much as possible because when you win, you rank up faster as far as level (i.e. Rank Track) but also there is a second progression track for Crowns (i.e. Crown Track). Both tracks give rewards which can be clothing items/patterns which are needed for this achievement, Kudos (in game currency for buying more clothes), name plates, emotes, celebrations, nicknames, or Show-Bucks (paid currency used for buying premium items in the store).

Three options for attacking this achievement:

1) Slow but Free Way - Play the game and rank up the slow and steady way by unlocking costumes pieces through the rank progression. The first sight for each uncommon or higher piece is listed below if you DO NOT have the Season Pass:

Rank Track
Level 21: Starry Cheeks (Pattern)
Level 53: Sapling (Colour)
Level 89: Hungry Tungling (Lower)
Level 95: Crabby Cappy (Upper)

Crown Track
Level 2: Kingswood (Colour)
Level 4: Rosette (Pattern) - Epic
Level 10: Crocodile (Lower)
Level 13: Crocodile (Upper)

2) Faster but Costly Way - Buy the Season Pass and unlock costumes more often. The first sight for each uncommon or higher piece is listed below if you DO have the Season Pass:

Rank Track
Level 1: Nyandroid X (Lower)
Level 2: Nyandroid X (Upper)
Level 21: Starry Cheeks (Pattern)
Level 53: Sapling (Colour)

Crown Track - Same as Option 1
Level 2: Kingswood (Colour)
Level 4: Rosette (Pattern) - Epic
Level 10: Crocodile (Lower)
Level 13: Crocodile (Upper)

3) Fastest but Most Expensive Way - Go to the store and just buy the pieces you need. Most items sold in the store using Show Bucks are Uncommon or better.

Once you have all items Uncommon or better, put them on by going to the third option at the top of the main menu (the coat hanger), select Outfits, and equip the pieces. Achievement should pop!

Common < Uncommon < Rare < Epic < Legendary
(Comment if these are wrong, also if you know where Special or Event fall into this...)

Season 1 Solution (old)
The quickest way to get this is to link your Amazon account to your profile by going to Settings on the main menu by pressing > Profile > Link Amazon Account.

As of Season 1 of Free for All, this will unlock the Summertime Activities Bundle which will give you the following uncommon items:

Pitchers Mitt Accessory (Upper)
Pool Life Line Accessory (Lower)
POP (Pattern)

The last thing you need is a Colour which can be unlocked by playing the game getting Fame, which is given to you by playing, winning, and completing challenges. The first uncommon Colour that you get in season 1 is Pumpkin Spice at level 27.

Once you have all of those, put them on by going to the third option at the top of the main menu (the coat hanger) and selecting Outfits. Achievement should pop!

If you do not have an Amazon account to link to, then you will want to check the store daily to see if they sell any uncommon items. Also, for Season 1 here are the first Uncommon items for the achievement pop up:

Level 20: Shape Up (Pattern)
Level 27: Pumpkin Spice (Colour) as mentioned above^
Level 12: Dragon Dance Head (Lower) - Epic Costume (I think epic is technically higher than uncommon)
Level 13: Dragon Dance Body (Upper) - Epic Costume