Find a ledge that you can shoot from but that they can't reach. Use enchantments on the bow and/or potions on the arrows. If they come after you and reach your ledge, you may not be able to outrun them in a straight line, but you can outmaneuver them around
a rock formation. Probably best NOT to fight them in the early game. Just get away and set up your next ambush attempt.
Shoot'em in the knee! That slows them down. Or when their scratching their backs, put one in the armpit. lol
*Pictures 2 giants sitting by a bonfire, talking*
...I used to be an adventurer giant like you...
All I remember is my first encounter, back when everything was so intimidating and unknown. After the Dragon ate me, I tried exploring and the Giant sent me into the starrey night sky like a rag doll. So anything is possible in this world. lol
or "I've been hunting these fields forever, the Jarl can't eat all the deer now can he". lol
At Silent Moons Camp there is a beehive looking structure. Tease the Giants and Mammoths and then run for that. You can hide in there and shoot from safety.