It can be difficult to play her solo top since she isn't as tanky in comparison to other champions that deal the same amount of damage or more. You will often want to play defensively and last hit what you can under your turret. This can be challenging since she is melee (some opponents, like Darius, may try to dive you while under your turret), but remember that you can use your Q to quickly jump to minions for the gold. Just make sure to immediately retreat afterwards to avoid being punished by your opponent.
I usually start with cloth armor and five health potions for sustenance. On your first trip back, you want to pick up Boots of Speed and another component of Wriggle's Lantern, which depends on if you're playing defensively or a bit more offensively. Grab a Vampiric Scepter if you're playing defensively, or a Long Sword/Madred's Razors if offensively. Move on to finish Wriggle's. Now you want to evaluate what your situation is in the overall game. If you find that you are having trouble staying alive, build a Phage for some defense. If you are doing just fine and you want more damage, save up for a BF Sword, although I will generally build a Phage anyways just to make sure I start building up my defense for late game.
You eventually want to have a Frozen Mallet and an Infinity Edge later in the game. Always build IE instead of Bloodthirster. Your Wriggle's will already provide you with enough lifesteal. If the game goes on long enough, pick up a Phantom Dancer or Guardian Angel, depending on whether you need to be more offensive or defensive, respectively. You could even sell your Wriggle's for a Bloodthirster, but usually the game will not last long enough for you to do so.