i think i'm on the opposite end of the spectrum - trying to put on weight if anything but it's important to try and maintain a low body fat % too
i would seriously recommend hitting up the gym 3-5 times a week if you have the time, cardio or weights. i don't do gear but there's a noticeable difference from what is really just a few months of work; it's also quite enjoyable and it really helps with the self esteem (let's face it, likely a problem for most of us). if you're doing solely weights, make sure you're pushing yourself and doing a workout that includes some high rep exercises or even some supersets. i was recommended this workout by a friend:
http://outalpha.com/the-out-alpha-novice-program/. more for building strength but it was a good place to start (does ignore shoulders + calves though.)
workout A:
Box Squat 3/5×4-6
Floor Press or Pause Bench 3/5×4-6
Pendlay Row 3/5×4-6
Overhead Barbell Extension 3×6-10
Barbell/Dumbbell Preacher Curl 3×6-10
Stiff-Legged Deadlift/Good Morning 2-3×6-10
Weighted Plank 3×30-60s
workout B:
Box Squat 3/5×4-6
Paused Overhead Press 3/5×4-6
Trap-Bar Deadlift 2×4-6
Close-Grip Bench Press 3×6-8
Weighted Chin-up 3×3-5
Weighted Plank 3×30-60s
hit it 3 times a week and just alternate - so A, B, A, then next week B, A, B. food wise, i think
what people above have said is pretty
spot on. drink water - i dilute mine a little bit with some juice. for
meals, do some basic cooking. i think a good formula is 3 parts: 1 protein (white meat or fish), 1 carb (bread or rice, etc. go wholegrain) and 1 bit of veg. this page has some great examples:
http://roamstrong.com/the-nomad-diet/
work out how many calories you need and chalk it up roughly, doesn't need to be an exact estimate. i feel using all of the apps and shit is a little unnecessary unless you're really serious about it.
this is just (very) amateur advice, but i started exercising properly nearly a year ago now and it's paying off already. i'm bulking rather than losing but i think i've managed to cut off at least 1-2% of body fat by being more conscious of what i eat and drink - and that was from probably 14% body fat maximum. you don't need to be super serious but stay committed to it overall and you'll see results in a few months of time. whatever you do, good luck and i hope it goes well