5'10, 168lbs here... I have the opposite problem... how do I put on more weight? ?!
What is your age, experience, and goals? For younger guys I honestly don't recommend going too big too soon. Getting the right plan and form is more important. Consistency is most critical. Some go hard out of the gate and then fall off a cliff.
Consistency is why you see some older guys in the gym who are outpacing the young guys. I was lifting in a gym about 4 years ago and had maybe 275 on the bench and some guy asked if I wanted him to spot me. Talking to him afterwards, it turned out the guy was over 70 years old and you would have thought he was an in shape 50. That only happens with consistency and that's some true motivation for me right there. He obviously knew he could pull 275 pounds off of me if I had trouble with it.
Everyone has a different mindset. I remember working out with a 6"2" 230lbs Marine who was early 20s as an undergrad at PSU after he had served. He could lift the house and I thought he should just maintain size but he said he wanted to be a freak. I didn't get it.
As for routine, I like to break it up in push days, pull days, and leg days. If you work the same body parts each day then you aren't allowing recovery and just keep breaking the muscle tissue down. So I usually do:
Day 1 PUSH chest/triceps day - Flat bench, incline bench, (you can do decline as well), flat and incline dumbbell press (these are important to work stabilizer muscles as you rarely push at the exact same angle in everyday use), flat and incline dumbbell flys, triceps push down with a cable machine, triceps kickback with dumbbells, close grip bench, etc. You don't have to do all if you don't want.
Day 2 FIRST LEG DAY which has heavy multi-joint exercises like squat, deadlifts, and leg press (although some do not recommend this including I believe Galt's staff due to the angle of your pelvis and pressure on the lower lumbars). I usually do calf raise as well from the leg press machine by sliding the feet down to the bottom of the foot hold so that the heel is off of the hold but the balls of the feet are still on them.
Day 3 PULL DAY (back and biceps) which starts with weighted pull ups (or regular ones or you can do assisted pull ups), then lat pull downs, then low rows, then some other type of row maybe with a T-bar or using a dumbell, then preacher curls, then seated and/or standing dumbell bicep curls, then I like to do the back hyperextension for the lower back.
Day 4 PUSH shoulders (this also works your pectorals and triceps like in day 1) which starts with shoulder press and/or dumbbell shoulder press (don't do them with the bar going behind the neck, too much strain on the shoulder joint), upright rows, shrugs, front and lateral raises (I prefer with dumbbells), rear delt (there is usually a machine that also doubles as a pec dec but just sit facing the seatback for this exercise), you can also do I/Y/and T which is the shape that you make in moving very light dumbbells while facing chest to an adjustable bench at maybe a 30 degree incline, you can also do scaption with light dumbbells (great for strengthening the rotator cuff for baseball players, QBs, etc).
Day 5 SECOND LEG DAY has more single joint exercises and I like to do some plyometric work. You can do leg extensions (quads), leg curls (hamstrings), calf raises (seated, standing, on the leg press machine as above or simply grab a handrail on the stairs and do one leg calf raises with or without a dumbell in the other hand), box jumps (you can do these straight on or side to side), bounding, power skip (as high as possible), or any other plyometric loading of the leg muscles.
Day 6 ABs and Cardio focus. You can do these every day to some extent but this is really just a day for me to focus a bit more on it than usual while giving other body parts more rest.
Notice that there is 2 days rest following each PUSH day, same for LEG days, and same for the PULL day. You need those 2 days for torn muscle fibers to repair and more muscle fibers and neurocontrol to develop. When you first start lifting, good form is so important because your neurocontrol develops first to learn the movement and then become more proficient at controlling the muscle fibers to execute the movement more efficiently. Then you start building muscle memory for the movement and you will see some good gains maybe after a few weeks or so. At that point you can add some more weight but make sure you maintain good form. You are building the foundation.
I would recommend 3 sets of each exercise at a weight that you can do 8 to 10 times after a warmup set of a weight that you could do 15 to 20 times (just so your muscles are warm and stretched, you don't have to do the warmup weight that many reps, it is just to give you the right idea for weight for the warmup). If after doing this for a few months and you have good form and built initial strength you decide to do more power lifting then have at least 1 or more of those sets be a weight you can only do 4 to 6 times. If you are going for more tone do your sets with a weight that you can do 10 to 15 times.
Oh and it is recommended to do a 15 minute cardio before starting to warm up and loosen your muscles. DON'T DO STATIC STRETCHING (holding a stretched position) before lifting. Your muscles need to be warmed up dynamically by moving at a lower pace so you stretch the muscles some but not too much. A light jog on the treadmill, arm circles and other movements specific to whatever body part you are going to lift are helpful to loosen up those muscles without overstretching and tearing muscle fibers (that's what a cold static stretch would do). You can work the static stretches AFTER the lift while the muscles are warm, pliable and can be part of a cool down. Doing too much too fast on static stretching may hold back your lifting gains.
I said before that I'm now middle aged so I don't go hard every single lift anymore. I do day 1 hard (fewer sets, fewer reps, heavier weights), day 2 lighter (more sets and more reps with lighter weight), day 3 hard, day 4 light, day 5 hard, day 6 is not really a lift day so it doesn't apply so much, then the next day 1 is light, day 2 is hard, etc.
Here's a great website to learn and doesn't just apply to gaining weight or lifting but is geared to overall fitness.
ExRx.net : Home Try clicking on the very first link
ExRx.net : Exercise Directory, it has every lift you really would want to do categorized by body part. When you get to each exercise for example
ExRx.net : Barbell Shoulder Press, it has a video of the correctly performed exercise form and some additional instructions and comments.
Good luck!
