Let me make this crystal clear to all of you who are new to ADC or are just ignorant

Unless you are Kalista (this champion -> ), who is arguably the best ADC to have boots on with high attack speed, #1) DO NOT EVER GRAB TIER 2 BOOTS AS A FIRST ITEM #2) DO NOT GET ATTACK SPEED BEFORE DAMAGE

Sure you may work well with some attack speed items (mainly the zeal ones), but if you just get attack speed with no damage, you will lose every trade, then the lane, then the game. Especially if you have an engage (not high damage) support like who can't really make up for your lack of damage since they offer nothing to you in terms of defense (champions like can at least lantern you out of a bad situation and/or shield you from / boost resistance to some of the incoming damage). But still do not use this as an excuse to build attack speed first.

Now, you do not necessarily need to finish a full damage item (though some recommend you do). You need to at least get a damage first. are the 3 items I would say you should always look to get first (depending on your first damage item). Then get your boots and attack speed, or finish the damage item. If you are building . Get before because not only does it have sustain and damage, but it also has a useful active. Sure has 15 damage on autos, but you are not dealing 100% of your damage through only auto attacks. Even on who like to have a lot of DPS over raw damage. Also, last I checked, 25 AD is better than 15 damage in at least the early game when no one has any defensive items, though I would say it always is better.

Do not give the enemy a free win because you did not build any damage.