the symbiote protected him on top of his spider-sense (physically moved him from danger as the spider-sense went off, Peter moved on the symbiote's "instincts" as opposed to being warned by the spider-sense and then moving in accordance)
Spider-man became a much more vicious and agressive fighter (intimidated enemies)
The symbiote created webbing when spider-man ran out
Now, depending on which title you read and who wrote it, the symbiote either gave spidey more power on top of his spider-strength or was bonded to him due to his already strong spider-sprength (prefered peter)
The common ret-con is that the symbiote enhanced his power/agility. I believe this was placed after it was shown that Venom was stronger than Spider-Man. Although an argument might be that if both had been normal humans, Brock would have been stronger than Peter anyways due to his size and the symbiote is only bringing Brock up to par.