So against tanky tops, despite your passive there going to be tough especially till you get a lot of bonus ad, so against them its best to poke down with q on a vital then get out with the speed boost then repeat, phage helps a lot against tanks due to the speed boost and health as it makes you slightly harder to kill. Against voli its not too terribly hard to get the w stun, but its harder if you jump on his face because then hell get an easy flip that could be hard to block. Tryndamere is difficult especially at 6 because your heal is not enough to last his ult, but if you fight him and you both ult just run a bit and if he stays to farm you can generally get him. Against squishier match ups like Riven or Tryndamere(hes not tanky just has a lot of sustain) i rush Ravenous Hydra into Trinity Force for the wave clear, sustain, and the health from phage, and sheen proc. Those items against match ups like that seem to help a lot, also Ninja Tabi are good on her in those match ups.
For combos pre 6 a good, at level 1 Qing towards a vital with a follow up AA is good. At level 2 do the same as level 1 but after the follow up AA if you use E to auto reset it does some pretty good damage. At 3 the same thing works but use w to counter them. if you repeat the 3+ combo twice it can generally kill them with ignite but careful because Fiora is pretty squishy early and its important to note its hard to go all in pre 6 and most champs can turn on you, so just do several trades instead of one all in.
Post 6 if you're next to them or then engage on you, depending on the opponent if its say Voli and he q's you when hes very close and you're positive you'll get the stun R him then W and you'll get one proc + the stun, then walk to either side AA, Q behind him get that vital and either AA reset with E and get the slow when you're behind them or run to the last side and E them then then finish with AA's and ignite.
Note your passive doesn't do too much early so a full ult if you have Tiamat or Phage is 16-20% of there hp so a lot of your damage is going to be coming from AA's and Q/E, w's cd is too long to be used more than once so use it intelligently.
For Match ups Vlad and Malphite are hard, Riven Vs Fiora is the epitome of a skill match up, and Kassadin is a very good match up for Fiora.