Sending cold emails shouldn't be the black art that is supposedly is. If you need to improve your emailing skills (cold or otherwise), you really need to be answering one question. Why? Why are you sending the email and why should the recipient read it?

It doesn't really matter what your goal is. It normally falls in to the following buckets:

- start relationship (cold opener)

- maintain relationship (information/email series)

- click on a link (signup/purchase)

All these are about persuasion. Many of Caldini's principles still apply: Reciprocity, Commitment and Consistency, Social Proof, Authority, Liking and Scarcity. (I would add Empathy to that list). However, more importantly, you should be providing something of true value otherwise, you're just spamming.