Well, this a hard question to truly answer as there are 3 different branching theories and I sit in the higher skilled minority, camp.
But, generally I'd say pick a big first.
All bigs inherently are the culmination of their ship tiers, so they will all borrow elements and exacerbate the weaknesses of their smaller sister craft.
The Vette is a fat Gunship with FAS pitch and FDS drift.
(She still keeps the OP vertical thrusters and acceleration + deceleration of her smaller sister, the FGS, but trades off the lateral and yaw that makes the FGS more agile than the FDL.)
The Cutter is a overblown hunk of trader junk, that has strong shields, but is the least agile of all 3 big ships.
You don't have much going for you as she puts all her strength into forward boost momentum and comes out with turn and boost lag, a massive turning circle, and very unresponsive thrusters.
"How to Cutter: Throw that Shiz in Reverse"
-Farsight Enclaves mocking Cutter pilots who die to our builds and pilots in 4 minutes.
The Conda is the culmination of DeLacey's attempts to make Combat ships.
But, she basically is a fat Python that actually Pythons.
(In comparison a Python can barely combat inside her tier.)
So, once you have chosen your big, then I'd guess it comes down to the style of play you fancy:
Cutters favor gimbal and turret weaponry while operating in large packs with massive shields. There's not much to her as she's pretty braindead, just don't let people with plasma stay on top of you too much as you'll get melted by absolute weaponry, despite your massive shield.
Corvettes are Time on Target monsters. They excel in hit and run, range control, and high alpha burst of damage in primarily fixed configurations.
There are two methods of PvP Vettes, the Farsight Vettes which are armor tank hybrids, and the "META" vettes which are prismatic, premium ammo turret builds.
Either or is viable, but in well...different ways.
META vettes make good support gankers, and Farsight Vettes make good frontline attack ships that can handle 4 or 5 targets at once.
Condas are a bit of a mixed bag, since, generally high shield sustain builds get out shot by both the Vette and the Cutter, and alpha builds require just as much skill to run as the Alpha Farsight Vette configurations.
I'd say before you can go much of anywhere, you must first identify what you are capable of and think you can handle.
Then, make changes / builds / templates according to what you are confident you can handle.