Spiders are one of the easiest enemies to defeat in The Elder Scrolls: Blades. Spiders come in different sizes and the difficulty increases when their size grows but overall they are on the easy-to-beat spectrum.
Spiders are weak against cleaving and frost damage but resist poison, shock and slashing damage. One effective way I found to kill the small spiders very easily is wearing a Shield with the added effect of dealing damage on block/parry. This way when you block the attack of a small spider they will take enough damage to hurt or kill themselves.
The small Forest Spiders use a special dynamic to attack which consists on stepping back for a period of time (during this time they ignore any melee attack you make) and right when they throw at you for an attack is when you can swing your weapon and punish them.
The big Spiders don’t use this special dynamic so they are vulnerable to melee attacks at any moment. This comes with the disadvantage that their health is increased considerable compared to the Forest Spider.