Increase your rare drop rate

This was something I learned the hard way on ME3 and so far has worked now that i've started on ME:A MP.

Initially and I'm sure many have been or are continuing to do so, are  focusing on purchasing gold and premium cases. Sure you get a high chance of getting rare or ultra-rare, but do you really want to take up those odds with so many common and uncommon items that can reduce your chances? Better your odds by thinning out the common and uncommon items (characters, weapons, mods) by purchasing basic crates (5k per) You unlock at least one maybe two commons and if you're lucky even an uncommon. Initially I was getting just commons but now that i am almost maxed out of common items, basic packs are now giving uncommon at a higher rate.

I expect, just like in ME3, that the basic crate will eventually become an exhausted resource only giving out supplies and boosters. With majority of maxed out common weapons and characters I've been able to play silver and gold with a high rate of success which in turn used to buy more basic crates. The idea is that by the time I begin purchasing silver crates I'll be able to unlock more uncommon items, maybe even gold at a higher rate, cheaper price and not worry about a common item taking up a slot. 

In a nutshell, buy basic packs until common items are maxed out and begins giving you uncommon. Once uncommon is maxed out, I believe you will be able to unlock a gold item through the silver crate at a higher rate, etc. going up the crate list.