A wise and talented instructor once told us, "it's not how deep you go, it's how you go deep"
Deep massage is NOT "no pain, no gain".
Remember, "deep tissue" means VASTLY different things to different clients--and therapists!
Don't use as much lubricant, as a general rule. Of course, I tend to break this rule, because I combine all techniques (including--and especially--deep tissue) with the use of hot stones. And the stones require a lot of oil. But I also carry a small "working" hand towel with me to dab any excess oil if necessary from the client's skin before attempting a deep techinque.
Use your body weight
Begin with jostling/vibration/heat/gentle myofascial release/etc (AKB is right on, regarding the rocking!) before going deeper. This does wonders--for you AND for them!
Also, I apply static and very subtle multidirectional friction with supported thumbs to muscle attachments. This is particularly useful for loosening up the upper traps (when I do this to the superior aspect of the spine of the scapula), or other areas like the common flexor tendon of the forearm, the distal tendons of the hamstrings, and even the achilles tendon as well.
Well, that's all I could think of for now. I'm off to bed
Hugs,
~Jyoti