So you want to kill that pesky Deerclops with your friend? Well, you're gonna need some help.
The easiest way for you to defeat him is by chopping as many trees as possible in Autumn. If a Treeguard appears, it's a good thing. You'll have gathered plenty of pinecones from that, so he'll become your first line of defense after appeasing him. Since the Treeguard will dwell around, there's no need to make wood walls as a waste; instead, go find a desert area to kill some Hounds, Tooth Traps will help with the Giants and keep your stuff safe from them.
So the mighty Deerclops has fallen, and you're stuck with some Living Logs from the Treeguard, and Meat from the Giant. If you or your friend is Wilson, wait until winter is over to shave. Meat Effigies are useful for the next few monsters. You're ready for whatever you need to face, until you realize you've been depending on forces of nature. By now, you've explored from kiting the Giant or chopping trees, and have stumbled upon Merm villages or Pig villages. Either way, you need some Pig Skin for all kinds of things, and one being a Football Helmet. Preparations are always needed for the Giants, so I recommend two different bases: a small one with a weapon chest and a fire pit, the other for everything you want to keep. If I missed anything, feel free to edit. I only made this because I got mad from losing to a Deerclops on DST. Enjoy!
Tooth traps + road technique Edit
in order to do so, try to collect as many hound teeth as possible (e.g killing Hounds when they periodically attack, or those which can be find in the desert. You can also search for someWalrus camps in order to gather many teeth dropped by the two blue hounds, as they always give you two teeth, and try to get a Walking Cane and/or a Tam o' Shanter on the same occasion by killing MacTusk.)
When you have some hounds tooth (around 20-30 would do it), find a straight road and set your tooth traps all the way. When the giant comes, go on the extremity of your road and wait for it, then you just have to kite it with the help of the road - which makes you walk faster, so avoiding the giant's relatively large AoE attacks might be easier.
By kiting the giant's attacks, it will walk on the road and activate the tooth traps, making additional damage to the giant. Your teammates can help you killing it by hitting it with you, or simply by resetting the traps after the giant's passage. When you hit the end of your road, you just have to repeat the process until the giant dies. Note that using an Ice Staff to freeze the giant or a Pan Flute to put it to sleep might help you to kill it, because it allows you and your teammates to hit it many times before the giant wakes up/attacks again.
Note that you can use this technique without tooth traps, which will just make you fight longer. During winter - when you have to fight the Deerclops - roads are covered with snow, making them difficult to follow ; the tooth traps can also help you to see it.
Also make sure everyone has some healing items, such as Honey Poultice, Jerkies or Healing Salves. You can also make some Telltale Hearts before the fight in order to resurrect your teammate in emergency without losing precious health during the battle. You also have to make some additional armors (such as a Log Suit) and Helmets (such as a Football Helmet), because you might destroy the one you wore at the beginning of the battle, since armors have less durability in DST.
To finish, note that Hounds might attack you during your battle against the Deerclops, which can be quite unsettling - in order to manage with them, you can let your giant kill them, or use an Ice Staff to freeze your giant and deal with the hounds with ease, even if the freezing effect is temporarly so you might hurry up.
Gunpowder technique Edit
You can kill any giant quite easily using some Gunpowders - although you will need much more gunpowder in DST because of the giant's increased health. Just make sure you don't kill the giant with your gunpowder - otherwise its loot will be burnt : you have lower its health as much as possible without killing it ; then you have to hit the giant a few more times to kill it.
In order to be sure to hit the giant with your gunpowder, use an Ice Staff to freeze it or a Pan flute to put it to sleep, place the gunpowder the closest to the giant as possible and ignite it using a simple Torch, Fire Staff or Willow's Lighter.
Below is depicted the number of Gunpowder you need to weaken the giant and leaving it with the minimal amount of health without killing it :
Deerclops (4000 health) : 19
Goose/Moose (6000 health) : 29
Bearger (6000 health) : 29
Dragonfly (27500) : 137
If you want to kill the Deerclops using gunpowder, you need to hurry up in order to craft them - because it spawns on day 30. You will need 19 Rotten Eggs to craft 19 gunpowders. Indeed, an egg turns into a rotten egg in 10 days during Autumn, and 12,5 days during Winter. Make sure to have a bird inside a Bird Cage (producing two eggs everyday if you give it food) as soon as possible, in order to have 19 gunpowders on day 30.