I, too, have that 20 lbs and have just started to really address this concern.
So...just a couple little things that I am adhering to:
Different thoughts on this subject but... DRINK lots of water. Try drinking NO LESS than 12 oz. glass around 15 minutes before each meal - to get the stomach acids prepped. I have always thought it was good to drink water with my meal but I was told by a dr. that it actually is more beneficial to drink it before the meal and to only sip during a meal. Also, when you wake up in the morning, first thing to do ... drink your 8 - 12 oz. water. The formula that I have been using (and there are a few different thoughts about this is) Figure your body weight; divide number by 1/2 and convert that number into ounces and THAT'S what you should drink in a day. (150 lbs divide by 2 + 75=ounces of water/per day or approximately nine-ten 8 oz. waters.). If you are concerned that you are going to have to go to the bathroom a lot, add a touch of sea salt/kosher to your water. You won't taste it - but it will curb your bathroom needs.
Also, write down what you eat -even those few pretzels or crackers that NEVER made it to a plate but get eaten on the fly - it really is amazing how many snacks I was able to "justify" having and once I wrote them down, I was a little shocked.
One of my friends is a personal trainer. She recommended to me that, even if I think I know what a "portion" looks like, for the first few times, measure it. So if it says.. you can eat 15 cheese nibs or 3/4 cup of cereal, measure it out to get that "true" measurement". You may be surprised how wrong your estimations have been - I know it was an eye-opener for me.
The personal trainer idea is a great one. You may only need someone for a few sessions but it will get you on a good exercise regime. If you are doing the same thing the same way... your body just gets used to it.
Also... use the buddy-system so that you make someone accountable who wants to lose weight and they make you accountable. It's great to have a cheer leader in your corner when you need one - (or that good friend who knows how to motivate and push you!)
Also... just think - if you lose 2 lbs each week, by the last week of March, you will have lost 20 lbs! Even if you go slower, easily by the end of April... WE CAN DO IT!
GO! GO! GO! Good luck.