I have a terrible time grounding too..and once out of practice I have to start in slow steps. But, there was a course my co-workers told me to go to..I couldn't afford it, but found the CD's online (can download mp3-or whatever it is called)
I did that on a fairly regular basis- one tape in particular. I can send you that info/link.
I think you techniques are good- I did that too, but it wasn't enough for me when I really pushed myself. (Like work got hectic). So I would listen to the tape prior to work, and then before a patient came in I would picture all of the energy running slowly into the ground..sitting I would try to get it to my butt..then butt to floor..into floor...grow roots. If I started out good at the beginning of the day I could do this in 30 seconds. Breathing too. Then I would continue it and shielding during the session. I got to realize who would drain me more..and who less..so that helped to prepare. I would then ground patients too so they could heal..and so we both wouldn't be flying high..LOL.
I think the key is to get as grounded as possible prior to a reading. then, once you start your vibrations will get higher as you ask for assistance and guidance.
Many people do the grounding and shielding..then picture white light coming from their "source" into the top of their head. Everyone's source is different- mine is God. So, that helps with the spiritual and protective component, while the other things (like you and I mentioned) help with the grounding. So, you want to ground so you can feel when you are getting too high (OK during a read to get higher) but then you have to go back down to replenish. If you aren't grounded, you don't recognize when you're not- at least for me.
I can see going from work and reading on a lunch break would be very hard to be centered. I had to eventually work out of my home and do my "stuff" in between patients. So, maybe no readings on break..you see and try things and find what works for you
http://www.healingfromthecore.com/products.shtml
I recommend healing from the core- Basic relaxation and energizing exercises
I have all 10 tapes..still mastering tape 2-LOL. This one focuses on grounding.
Sometimes when I am too ungrounded to sit and meditate..a nice tape was one that had you listen and walk. that put me a bit lower to eventually get to the meditation point.
http://www.healthjourneys.com/MainCategory.aspx?mcid=1
Meditations to relieve stress..Belleruth Naparstuk
The one I like is a walking one..just has you look around as you walk..takes the mind chatter out. Prepares you to meditate if life is to hectic.
Maybe someone else has ideas
Getting outdoors helps a lot too..at break or before reading.
I hope some of this helped