You gotta be more specific about what you mean "in really good shape", and if you did mention it... Yea I just didn't bother to read the other pages. Me for example, from my dads side they're not fat. Like it's hard for me to gain weight, but I'd like to gain more muscle weight so thats my goal, and plus I like kick boxing so the workouts I do may or may not be usefull for you. So it all depends and what your goal is. Like do you want abs? 6 pack? Are you the type who gains weight fast? So set your goals, see what it is you want do and then go from there. Most of my workout is with dumbells since I dont got time to go to a gym, and using dumbells for your workout is pretty good, it's helped me. I don't do that much cardio and thats cause I'm a bit busy to do much cardio, but if I can I'll run for 20 or 30 minutes so thats for my cardio. Once you know what you wanna do like, gain more muscle weight, or get lean or w/e your goal is, then start looking at the workouts that you would need. If you're the type who who wants a 6 pack, thats something that you cannot easily get, and a lot of people lose hope if they dont see a six pack in like 4 months. You dont need a personal trainer, but if you got the time go to a gym.
right now, im 5'10", 170 lbs, bench 150 lbs, and have an almighty six pack. it helps that i've been swimming competitively since age 4 and was 1 step below olympic level (not in the US) before i retired to go to college. i was even fitter, bulkier and stronger then than now. i would NOT recommend bulking up. ever. especially if you're naturally incredibly skinny. (which you are.) do you want to find out what you'll look like when you;re say, 45, when all the bulk has pretty turned/turning to lard? not to mention the health problems that come when its not your natural size. at 24, im already feeling the disadvantage of bulking beyond what i should be. because, without regular use (and as a working pr0fessional, its near impossible to maintain a level of activity that i used to), muscle is getting replaced by fat. not a nice feeling. so work on your cardio, stay fit, get your six pack, get strong (strong is always good), but try not to double in size to impress the girls. if ye're still growing, height-wise, i wont recommend working out. make a few routines, try them out a week at a time at 70% intensity and find 1 you're comfortable with.
If you're the type that easily gains weight, lift heavy. If you're naturally skinny, then just stick to cardio and light weights with high reps.
