you have to do full-body workouts and keep changing your routines so your body doesn't get used to it and adjust to "preserve" and protect itself from strains.
you have to build up muscle and then do light interval training so that the built up muscle can burn your fat more efficiently. the more muscle you have, no matter which muscle, the faster you will burn whatever fat you have. so if you have 150 lbs / 30 lbs of muscle/fat respectively, and someone else has 200 / 30, and you both do the same exercises for 1 week, and everything else is kept equal (diet, rest, etc.), the 2nd person will lose more fat, because more fat will be used up to deliver energy to his muscles.
building muscle:
some of the most effective ways to build muscle are the most basic ones: pushups, situps, chinups (those are hard for me personally), and other similar exercises that don't require gym memberships, weights, etc.
for example, basic pushups work out primarily your chest and triceps, which are 2 completely different muscle groups, and a bunch of other secondary muscle groups - forearms, a bit of biceps... it's quite incredible. you don't even have to do too many. do like - 10 every hour or 2 hours. before you know it (like a week) you're doing 20. then it's 30. this is from personal experience.
but to build serious muscle (not "ripped" muscle, but the one i was talking about earlier - just to build mass) you need to work your ass - gluteus maximus and leg muscles such as quads. they are the biggest muscles in your body and gain mass the fastest, i find.
now, this is important to lose weight: during your workouts - do the muscle workout FIRST, and only then do the light interval training (cardio). yeah - you need to do both in the same session. working the muscles will use up your stored-for-short-term-use energy, and when you do the cardio, your body will use up your reserves (body fat), since the stored-for-short-term supply will be depleted by then.
what is interval training?
there are many variations, but this is what i personally call interval training: you get on a treadmill, you're already warmed up from the muscle workout, but you can stretch if you want to. do about a minute warmup pace, then increase it to a light jog (for me it's 5.5mph, but i'm tall... for you it can be 6, or 4.5... whatever you're comfortable with to start. you'll raise it gradually anyway as you get fitter so it really doesn't matter what you start with) do this for a minute. then for a minute increase it to like 8mph - sprint. then reduce it back to 5.5 for a minute. then bring it back to 8mph for a minute. then back to 5.5 for a minute. keep going back and forth in 1-minute intervals for 10-20 minutes, whatever is comfortable for you. that's all you need. there is no need to run for 60 minutes - you'll just be burning your muscles away. you can change it up in other sessions to 2 minute intervals, or 1.5 minute cardio with 30 second jog, and so forth.
now, i find that when you do 10 minutes of interval training, time passes much much faster than when you do just 10 minutes of straight running at 6mph. it's an illusion, but it is true. usually i'm like "wow, that was fast."
as you get in better shape you can increase your jog to 6mph, and your sprint to 10mph. up to you really. you'll get bored of 5.5/8 within a few sessions ... i.e. it will simply be too easy for you.
anyway, this is a starter routine that is guaranteed to get you results within 2-3 sessions. yes, i said guaranteed. even if you don't work on your diet, you will see results. though you will also start eating healthier because psychologically after seeing results you wouldn't want to see these hard earned results be thrown away because of McD's, so you'll be pulled into eating healthier. it's like a snowball effect. within a few weeks of this, even only twice a week, you will see nice visible results on the scale, in the mirror, and with your own eyes: you'll be more toned, clothes will be more loose, you'll feel more confident... etc.
i know it works for me, so i know it will work for others.
there are other things to do in the gym which i also do, but this is the beginner program and works great by itself.
i hope this helps
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EDIT:
i forgot to mention a very important thing: if you're just starting to work out after leading an unhealthy life style for a while, there is one thing you have to do first. basically, your body is completely out of shape, and your muscles are simply not used to any strain. the first time you will work them out they will get such a shock to them that they will hurt and have lactic acid in them for days. sometimes it can get so bad that it's hard for you to move them. for me for example, if i don't do biceps for a few months, and then try to do my regular 4 sets of 10 of like even just 20 pounds, right off the bat, i know that first of all my biceps will hurt for about a week, and 2nd of all, they'll curl up and i won't be able to straighten my hands at all for also about a week. that's just how it is.
what you have to do is to shock all of your muscles in your body, but gently. that way they won't hurt as much or will render you unable to freakin move, but at the same time they will "wake up" to exercise. so try to work out all of your muscles in the same first session. don't do too much weight and too many repetitions. even if you feel like you can push yourself to 100%, only push yourself to 70%.
after you do this with different muscle groups - inner thighs, quads, glutes, ham strings, calfs, biceps, triceps, lower abs, upper abs, lower back, upper back, chest, deltoids (shoulders) front/center/rear ... then you should rest for up to a week. your body will hurt from the lactic acid being particularly nasty to your muscles just because you haven't worked out in ages, or for some people, ever. this should pass after 4-7 days. once this initial shock passes, you can start going to the gym regularly and challenging yourself more and more. your muscles will still ache after the workouts, but nowhere near as much as they will after that first "wake up" session.
also, make sure you are doing the exercises with correct form so that you don't injure yourself. form is more important than weight.
i am wondering if anyone is going to follow this advice and actually lose weight...

i've been away from the gym for about 2-3 months and got completely out of shape. i'll be doing exactly what i wrote above as of this coming monday and can even update my results in this thread
