Ashe: Boots + 3 pots
1st back: 2 Doran's Blades
2nd back: BF Sword
3rd back: Bloodthirster and Beserker's Greaves
After that: Infinity Edge, Phantom Dancer, Last Whisper, Guardian Angel
THat's a cookiecutter build that works on ALL ad carries and the rushed bloodthirster's lifesteal leaves some room for error in engaging.
For Akali... Whoooo that's a big load haha...
First off, avoid engaging until level 6. use your Q to gain last hits
Also, you'll need specific runes and masteries for Akali.Namely 10+ AD from level 1 on for sustain and otherwise, AP and Magic Penetration.
Once you hit lvl 6, Hit them with Q, wait for Q to get off cooldown, R to them, E, Q, R, attack, attack, R, Ignite if you have to. That should burst down a large majority of ranged champions. Obviously the attack pattern changes with some champs, especially those with CC but that's more or less the attack pattern.
Also, don't forget about your W in engages! If you do end up in exchanges, your W increases your armor and magic resist, allowing you to take more punishment. Also, staying invisible can reduce damage taken while you attack in small bursts of Q+E, invis, rinse and repeat. The spellvamp from your passive will also make these encounters far less challenging. Also, if you rush a hextech revolver, it'll save you a lot of health.