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. 

----------

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).