Training to failure like FUTURA said is pretty key for quick gains, don't neglect muscle groups and try to stick to free weights, some of those machines are no good for your joints and you work out more muscle groups using free weights, and yeah, supplements are necessary, a lot of people swear by all the different brands but get some Whey protein and you're good to go.
Remember, eat smaller meals, but more of them, cut out fatty foods like burgers, eat lean meat like grilled skinless chicken, lean steak etc.
And a Lewis said, it's impossible to spot reduce fat, don't even try doing 200 situps or 50 squats a day in an attempt to reduce the fat off your arse or belly, it won't work, HIIT is probably the best way to lose weight, look that up there are some good articles about it floating around.
Last but not least, get a proper workout routine, don't randomly do weights, if you're doing a 3 day split make sure you hit all the muscle groups and have enough time to rest, rest is just as important as actually working out.