As I’ve mentioned in the weight-loss threads around here, I’ve recently dropped 65 pounds. I’d like to start strength training. I’ve gotten a decent home gym, and I’m just wanting some advice from the Dopers who are experienced in strength training. I’m interested in building muscle mass, not just toning up (I’m a guy, FWIW), so I know that I should be using higher weights and lower reps. However, I have no idea what muscle groups to train when, how often a week to train each group, which exercises are best for building mass, and how many reps are enough.
Help?
Can you afford a trainer / weight-lifting coach?
In my personal experience - having someone experienced design your workouts can make a huge difference. My brother hired a weight-lifting coach to train him. He dropped weight, and got significantly stronger all-over.
“Seek help” - just the type of advice you want to get when you log onto your favorite message board to seek help, right? 
FWIW My advice - make sure to work out opposing muscle groups (e.g. biceps & triceps), don’t forget your cardio, and stay off the juice.
Are you wanting to find a person to tell you cookie cutter routines, or are you more interested in learning enough to develop your own flexible and tailored routines you made yourself. There is a world of difference. My advice to you is learn as much as you can about what works, what processes it works by, what diet you need to set for yourself for your goals, and what sort of training you need to do.
There are many different types of strength training, and most of them do actually work. If you want to bodybuild, but are a boxer, it might not work out. If you want to get super strong, but don’t care about looking like a “pretty boy”, bodybuilding probably isn’t for you. If you want explosive power for martial arts or boxing, Olympic style lifts combined with lots of Cardio, stretching and plyometrics is probably best. Same if you are a wrestler. If you just want to be somewhat strong, look good, and be healthy with minimal chances of injury, bodybuilding or general weightlifting is just fine for you. Combine it with some cardio, switch it up ever once in awhile and you are good to go.
As a recent (two years) convert to fitness, here’s what I was told, and it works for me: find someone that looks like you want to look like, muscle-wise, who is friendly. (I did this at the gym; you may have to try harder to find a casual advisor… at work, maybe?) Ask them how they started out and what all they do. Then, you may alter the plan to fit your lifestyle/abilities, but pretty much copy them if you can.
It saved me untold amounts of money on personal trainers.
I’d need a little more information to point you in the right direction. Are you primarily interested in training for looks, or do you have something else in mind with looks as a second?
Probably the best thing you can do at first, is go to a gym. It really helps in terms of motivation, you can get help and encouragement (spotters) and you can also watch a little to improve your form.
Assuming you’re a beginner, you’re in good health, and you want to start right now, I’d go with simple exercises for the bigger muscles - bench press, shoulder press, pull downs and squats.
Start with little weight, do 5 to 10 reps, wait a couple of minutes, add 10Kgs, rinse and repeat. When you get to a weight where you can’t finish the set, stop ! Don’t work out the same muscles on consecutive days, drink plenty of water, get plenty of sleep, dress warm and always be friendly with strangers. Stretching after you finish will reduce next day muscle soreness, and is generally a good idea anyway. A few months of this should add a little mass, and maybe give you an idea of where you want to go next.
But you know, even keeping it that simple and unsophisticated you need somebody to help you with the exercises - where to position your hands, your back, speed of motions etc etc I see lots of guys (usually younger) doing some pretty hazardous stuff in the weight room…
Good luck, and enjoy !
Get yourself a copy of Getting Stronger by Bill Pearl. It’s basically a bible for strength training. He covers routines, training plans, and, most importantly, has line illustrations for literally hundreds of exercises organized by body part.