Falling Off...and getting back on again

I'm not sure why this time of year is so difficult for me.  Perhaps it's the classroom parties, the fields of fresh fruit (which of course signify delicious desserts), or just the feeling that I need to get my eating in before the summer hits.  The summer, to me, is kind of like the New Year's Resolution.  It's time for a fresh start.  As this week comes to a close, and the new one begins, I hope to keep track of what I eat, but to also get out each day.  I don't want to be a slug this summer.  I have to keep telling myself that my ultimate goal is to be in shape to hike in the Alps with Matt next summer, with a full backpack on my back.  First step - lose 10% of my weight.  I'm at 178 right now - so, 10% is about 18lbs.  That's a lot.  Ok, maybe a good first step would just be 5% - that's 9 lbs.  Somehow that seems more plausible.  Now, to plan on how to do that.