Akali is good mid, i dont know why ppls dont beleve that. There r just few rullez u have to follow:
NEVER be agresive. Stay behind your creeps, even if is necesery stay on the line for XP, and just last hiting with Q.
Learn to kill creeps on your tower cuz u gona get pushed there.
Wait for your chances. There r ALWAYS few before lvl 6. Because ppls r not used to play vs akali mid, they think she suck there and going too agresive vs her, usualy get few tower hits or punished by the creeps, but there r always moments where your oponent is 1/2 HP near your tower, u r on 70% and have rdy ghost + igntie = instant win.
1 time u get lvl advantage over your oponent there is nothink he can do to u.
After hit lvl 6 wait to get 2nd charge, and just kill your enemy, there is almost no chance for him/his to escape from you, or kill u.
Most important for Akali mid is to be patient. She can stay B because very easy last hiting creep with Q, also Q not have big CD so is almost everytime rdy . Also energy alow u to spam it forever.
TL;DR Akali is good mid, need just few games to use to her, and be patient.
P.S. Thats not mean to say to your Annie that u must be mid and send her sidelane, thats mean that Akali is not so bad, mid choise but rly she should let few other champs to go there if they r in her team (Like Annie, Kat, etc.)