Play Singleplayer - You probobly already have this
Play Multiplayer - Obvious, just find a server
Every Time Achevment (e.g Play game for a week, stay on server for 8 hours, ect) - Obvious
Meet Gary - Veeeerry hard to find him, and you obviously can't cheat achevments, I guess get lucky.
The 4 uploading related ones (e.g get 10 likes, get 100, ect) - I don't know how to traffic people onto the items well.

secret phrase - I'll just tell you, it's "bloxwich", and you type it in the chat window, or on comand prompt by using the say command, then putting the words in quotes (e.g [say "bloxwich"]).

Warzone, Innocent Bystander, Bad Friend - For these, you disable npc ai, then spam the npc to then get it, just remember to use the remover tool for all removals if you hav'int gotten the remover achevment. I just hold q, then while running backwords on flatland map, I spam that npc a little, then I remove them all. Once you got them all, or want a break, you can make the npcs think again.

Ball eater - go find them in entities, then fun & games, then spam the balls, and run around, spamming them with e until you get it.

Creator, Ragdolls - For creator you spawn any prop, and spam, then use the removal tool to remove them. I recommend hovering a little over the ground, looking down, then spamming a flat prop that can be stacked a little, then spam the remover tool on them while standing there. With

ragdolls, just be aware of the physics moving them when spamming, making it lag way more than with just props.

bad coder - idk how to help with this, other than find two addons that contradict with each other, causing the little error to appear on the upper left.

frendly - How many friends do you have? If you have 10, and al them have gmod, and they all are online at the same time, your golden, but if not, then go through and find some through steam, making sure ther active enough, arnt just throw away accounts, and have gmod. Go through, and find people with these things they have, and freind them. Now, set up a gathering on a server that's not crowded, and can fit 10 people on there, send them all access to join, and there.

Map loader - find 18 maps (you should already have 2 in gmod already) on the workshop, and browse and find ones you like. Then go through each one, and load them. If you already been in one, you don't have to go there again to get this.

play around - just switch to TTT on the main menu in the lower right corner, then start a singleplayer game.

popper - use the dynomite tool, and spawn it on a wall, then stick it to the wall by using the phys gun and holding left click, then right clicking. Now, switch to the balloon tool, and spam on the dynamite. Be sure you know what key you set it to explode to, step back a little, and hit it once, or twice. Most of them should go. Do this over and over until you get it

menu user - spam the q button to go into the spawn menu. You can make it better, if you have turbo fire on your keyboard. If you can't, but do have a usb gamepad, with turbo built in, download joy2key, make a new prefix, have the controller plugged in, hold down the button, and find the yellow glowing key. Double click it, then let go of the button. set it to q, then accept. Now go back to gmod, turn on turbo for the button, then hold it. You can do this while watching youtube!