Fiora's Passive can make a huge difference when trading with her. If you’re unhappy with the area marked, walking back a certain distance will reset the position.
Playing around Fiora's W is a focal point of the lane. Try baiting it out before you all in her to prevent her from neglecting your CC.
Keeping the minion wave closer to your side of the map will make it very hard for her to chase you down and kill you in lane. If you push and she freezes, you will be very vulnerable to ganks and all-ins from Fiora.
Fiora is a great split pusher and one of the best duelists in the game thanks to her Ultimate R and Q. If you can't match her in a side lane, try your best to force an uneven team fight on the other side of the map.
Fiora relies heavily on life steal. Buy a grievous wounds item early to neuter a huge part of what makes her such a good duelist.
Keep a constant eye on the map and the location of Fiora when you’re grouped with your team. If she goes missing, expect that she’s coming to join the team fight. If she stays in a side lane, don’t let her destroy your base while you try and fight.
Fiora is extremely good at level 1. If she gets the right Vital procs, she can cheese an early first blood or leave you chugging your potions at your tower. Respect her all-in potential and do not fight her early on.
When Fiora hits level 6 her duelling potential is fully realized. She can 1v1 almost anyone while her R is up.
Fiora is very good in the later stages of the laning phase and the mid-game. Respect her 1v1 potential and try not to die to her.