M.B.
In my experience and particularly since you are just getting into this a very gentle 7 day cleanse might be the best way to start. My favorite is the Zand brand that you can buy at Sprouts or Whole Foods (or online here):
http://www.iherb.com/ProductDetails.aspx?c=1&pid=4911...
It's quite gentle, but effective - it's also free of most allergens (i.e., gluten free - some are not).
Also, I'm assuming you'll add juicing at some point. In terms of veggies, it's best to start with carrots before adding beets, greens, etc. as it does take some adjusting of your taste buds. To remove sugar, stevia is an herb that's a good substitute. Also, I recommend one change at a time and it may take you well over a year to get to where you want to be - typically you have to stick with something for 6 months for it to be a true lifestyle change. And, everything reverses when you go back to old/unhealthy habits.
And, back to cleanse, they typically recommend you do one about 4 times a year (at the change of season). There are herbs you can take as maintenance as well. It's just that some of the cleanses do remove nutrients, thus you should not remain on them long term.
And, perhaps most importantly, you really should not attempt any of these changes unless you've had a recent physical, including CBC and CMP, EKG and bone density and have normal bowel movements. And, be very careful of products that claim to remove heavy metals if you still have any amalgam fillings - these products can increase the circulation of the heavy metals and actually cause more problems (e.g., impacting kidneys, etc.).