What triggers your ejaculation? Does an erotic mental image send you over the top? Or is it a mental thought? Or is it too much physical stimulation that sends you over the top?  Pay extremely close attention to what triggers ejaculation for you. Figure out what triggers your body to release sperm. For me, it's imagining fucking a hot, new woman. 

Your goal is to figure out how to approach orgasm with less pressure.

Typical triggers for ejaculation:

1. Thoughts of possessing her.   
(I make her pregnant - she is mine)

2. Fucking a new woman
(Fact or fantasy)

3. Hot, sexy thoughts
(I'll leave this to your imagination)

4. Thinking with the dick 
(Feeling everything in one place)

5. All forms of lust
(Packs all the energy into the penis)

6. Fast friction

You don't have to ejaculate. Ejaculation is triggered by some sort of over the top experience! Your first successful dry orgasms will be under the top experiences. I suggest reaching orgasm from the bottom, from less mental and physical stimulation, from beneath the threshold. Once you discover your triggers, you can refrain from the precise thoughts, images, or physical touch that trigger your ejaculation. 

For more tips: please read this book.