Whoever advised you on not to lift weights maybe gave you this advice with relation to your age at the time?
I'm presuming here that you were 16 or under at the time when you recieved this advice.
As for lifting weights... the higher repitition numbers you go for the increase in stamina this brings... lower reps with prolonged increase in weight brings out more strength.
So if you were a fighter who would say want to walk in the fight, knock someone out in 10secs then go home then you would require large amounts of strength/explosiveness... compound lifts such as back squats/bench press on low amounts of reps with heavy weights would achieve this.
Again presuming you are young here my advice would be to go down the stamina road as if you can outlast your opponent, it would be like fighting a little girl for her barbie doll when your opponent is tired... So high reps on a reasonablle amount of weight (something you can feel working your muscles but not exhausting them after 1-2 lifts)
so 4 sets of 15reps.... compound lifts such as barbell bench press, dumbbell bench press, front squats, deadlifts.
shifting your own body weight is good for MMA aswel, simple exercises such as pressups, chin ups, dips, wide grip and close grip chinups.
Try to seperate your gym visits to say 3-4 days, with one day being dedicated to say your shoulder/chest region, one day to your back region, one day to your leg muscle groups and a day dedicated to treadmill/cycling/swimming.
Before any gym workout spend atleast 10min with a casual jog on a treadmill, get warmed up... have a 1-2min rest after the treadmill, and stretch out say your upper body/arms region if you are planning on working that body region.
Try to keep your weight workouts to a max of 45-50min no more, and after a workout get on the treadmill and have a 10min run...
After working out try and stay under a cold shower for a few mins, preferably a bath where your whole body is covered in really cold water... go back into hot water and then back into cold water again mixing it up if you wish.
Oh yea i forgot try out some shoulder shrugs with dumbbells or iron plates with grips, good for the neck region = breaking away from the clinch and submission.