Through personal experience I build boots then work on an abyssal, the leg up that abyssal gives you is the early mres (i build negatron first) vs your most likely Ap mid opponent.
The advantage you have early is the low cd on your q allowing you to spam it to win trades versus higher cd mids ( anivia comes to mind ). In lane you want to be using a mix of q and auto attacks to farm last hits, (not aoe pushing) and your q through a minion to harass the enemy on the opposite side of it.
As the game goes on you basically have to decide whether to use your ult to get a kill in your lane (usually not the case because of flash and the small distance to tower coupled with the fact you need to keep your lane pushed) or to gank either top or bot. Depending on how well you are doing you will most likely want to finish your boots into the spell pen boots before completing your abyssal, at which point you have to look at the enemy team (and your own teams scores/skill) and decide what to build next.....
Rylai's - The enemy team is easily kiteable or you are comfortable in the timing of your w to remove slows and continue damaging while maintaining distance. Never underestimate a bit of early health.
Lichbane - Only if you feel like A) You really aren't going to get focused and will make use of the procs (not likely... yet) or B) Your team is not reliable for pushing down towers or grabbing objectives (Aka you have to be willing/able to carry)
Deathcap - You are far ahead and have a reliable fight starter that can displace or control the first few seconds of a teamfight to allow you to shine with your ults shield and superior damage (amumu, gangplank ult, etc..) *High Risk, High Reward*
Dfg is a good item for burst but isn't strong enough to justify rushing it for a flat AP value and an activation (glass cannon builds are very situational) , still this is definately an item to pick up a bit later into your build.
Skill order : qwqe maxing q first then e, taking points into r whenever available
Sample build: Sorc Boots, Abyssal, Deathcap, GA, Voidstaff, Rylai's / Dfg *no particular order here*
Misc: Blue (any cdr) becomes very useful at level 11 dont worry about giving early blue to mana intensive junglers.
Remember your passive and you will find it hard to oom yourself.
Farm lanes with q while the minions are lined up or create aoe situations for yourself through proper positioning, W removes slows placed before its activation.. not after.
Play your role appropriately in teamfights, kill the squishy adc etc..
Pardon any spelling mistakes, typing very late at night and tired doesn't bode well lol..