You should prioritize CS above everything else no matter who you're playing.
If you know you can best your opponent in lane, then focus on neutralizing them early. Generally top lane is called early. If you have room to be aggressive and proc vitals, take advantage of it. Be prepared though and always ward. A very small percentage of people will know how to bait you out when you try to hit a vital. Test that, and always treat your opponent like they're your best. If they are someone who plays like that, then it's better to just farm because you likely will not be able to kill them 1v1 until you get your items. Lane bullies are very effective against Fiora when they know her kit, so in that case it is better just to farm unless someone is ganking.
Do not rush Hydra, but finish it when you have a chance. Go for Tiamat as soon as you can. I do always end up finishing Hydra earlier, so it shouldn't be the last item you complete or anything.
Regular Build
3 AD Quints, 9 flat AD reds, 9 scaling armor yellows, CDR blues or scaling MR.
I switch to scaling health and flat magic resist when I'm against AP opponents.
Standard 21/9/0 masteries
Also when I play Fiora I generally use
for my spells as I am pretty aggressive during the laning phase. If you aren't comfortable without flash, then that's fine. Choose teleport or ignite.
I like these items on Fiora, but I rarely am able to get these same items together. They are just in the majority of my builds.
Choose between
and
. I like Trinity more, even though it's not as popular as it was 2 months ago. It gives you everything else you need to be a successful Fiora. I think
is good to get in some situations with Black Cleaver as well. Base your choice around your matchups.
If you need defensive items
are all acceptable too.
For boots I go
or
. CDR and tenacity are lifesavers.
What you build is ultimately up to you. I've tried many builds on Fiora with a lot of success, and many people do prefer to have at least one defensive item. I just prefer this one generally. I'm an old Fiora main, so maybe that's why I've become so used to a Fiora that just deletes people. I also main support, so if I'm not supporting, I want to play aggressive.
Cooldown redution, lifesteal, and mobility are my favorites on Fiora, and I generally see people do better KDA wise who focus on that. They allow you to duel effectively, stress your advantages, and stay onto people.
As a Fiora main, you're pretty lucky most of the time. A lot of people have banned her or refuse to learn her kit, so when she makes it past banning phase or you're in normals the chances of you getting punished for your mistakes are very slim. Practice makes perfect though, and you won't always have this situation. I say it's a great time to take her into normals and learn her.