Usually, when I play as Wigfrid in a server alone, before fighting any season giant, I make sure: 

- I can deal enough damage to kill them (at least 4000 damages in the case of the Deerclops) with my equipped weapon. For the Deerclops, that's around 38% of a Battle Spear durability as Wigfrid; it would take around 79% of a regular Spear to take him down with characters who have normal damage multiplier. 
- I have 2 or 3 helms available in my inventory, just in case (or anything that gives at least 80% damage protection). 
- I have at least 75% of my character's health (assuming you're not playing as Maxwell, since his health cap only at 75). 
- I have some healing items (preferably Healing Salve), just in case. 

Once I'm ready, I just rush in and attack. 

During the fight: 

- When you just started the fight, the Deerclops needs to hit you 3 times to freeze you. But if you already got frozen and he unfroze you by hitting you, the next 2 hit will freeze you. 
- Everytime the Deerclops hit you, you'll notice your character will get a "pale" tone, which means they're "freezing". Upon being hit twice, run away until the pale colour fades away before charging again, this way the next hit you take won't freeze you. 
- If you're playing with a friend, your friend should be standing on the opposite side of the Deerclops, this way you don't both get hit when he attacks. 
- Keep hitting him until he's dead. 

As I pointed out in the comments, if either of you is hosting the game (rather than playing in a public dedicated server), whenever something goes wrong during the fight, the host can type `/rollback` in the chat and press enter. 

This will allow you to start the game over from the last save (usually the last morning save, or the last time the host disconnected the server), instead of replaying the entire game again whenever you fail and/or die. 

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If fighting isn't a solution, when I hear a "warning sound" from the giants, I run as far as I can from my camp (if I have one). 

Once the giant monster has spawned, I leave him on that part of the map, this way he won't respawn on subsequent season (e.g. a new Deerclops won't spawn in the next Winter, if the previous one wasn't killed). You just have to make sure that nobody approach that part of the map (consider it a quarantine area).