Weight Training

A lot of people do antagonistic.

Chest/Back
Bi/Tri
Leg/Ab
And shoulders in there somewhere.

You could do upper/lower alternating days, you could do 3 days full body..

My old trainer had me doing biceps and chest one day, back, shoulders and triceps, and then legs another day. He had me doing abs 5 days a week along with some cardio.

My new trainer has me doing the same thing except the days that I train with him we do full body

From my experience, I did abs every day. However, if you can find workouts that combine more than one muscle group you burn more and reap more benefits. For example, If you are doing bicep curles, do them in a squating position or hold a small ball between your knees. It is a lot harder but you really feel the burn.

In theory it does matter how you group the "split" of weight exercises, along with the good ones suggested already, another variation is the push & pull routine split.

The push & pull split, involves performing all the pulling exercises in one session, then the following day performing all the pushing exercises. An iteration of this is to branch off legs & abs as convenient for you, so for example:

Day A: Chest, Triceps, Shoulders (Push-day, upper-body)
Day B: Back, Biceps, Abs (Pull-day, upper-body)
Day C: Legs, Abs
etc.

Some people put Abs with Back together, and Shoulders can also be moved around also.
Good luck~!

this is very similar to what i do.

chest/tricep
back/bicep
chest/tricep
shoulders/legs

some people prefer chest/bi so its a push/pull motion, but i prefer the same motion. ive also been doing chest/tricep twice a week because it is lagging compared to the rest of my body so i hit it twice. also, i like to have shoulders on a separate day so i can isolate it and hit it hard.

So I finally conquered my fear of using the weight machines with my fiances help. I always felt silly using them and they intimidated me, sounds soo dumb but it was a hurdle for me and I was only doing cardio. My question is I have heard that it is good to work out specific muscles on your body each day. I was going to group Ab's & Back together one day and Legs and Arm's together the next day and rotate that, I work out six days a week. Does it matter which ones you do together? Is it beneficial to do certain muscles together the same day? Thanks for your help!

Good for you, strength training is always a good decision. You can do various splits, there's no real right or wrong way to do it just find what works for you.

Here's an example of what I do, 6-day split too.
1. Mon: Shoulders w/ 30min light cardio
- Heavy military presses then supporting "lighter" shoulder work, tricep work, and Ab's
2. Tue: Squat w/ 30 min light cardio
- Obviously heavy squatting of some kind with lighter leg support work
3. Wed: Back (Lat's) and Biceps (this is low intensity so I exclude cardio and keep this day easy)
4. Thur: Chest w/ 30 min cardio
- Heavy bench pressing followed by lighter support work and Triceps, maybe Ab's
5. Fri: Deadlifting (Basically another leg day) w/ 30min cardio
- Heavy deadlifts with lighter support work. I'm actually going to experiment with plyometrics instead of additional weight lifting on this day.
6. Sat: Upper Back and Biceps

I try and combine some exercises for smaller muscle groups that also support the larger muscle groups. For instance, on my shoulder day I also do some tricep work because the tricep is a strong supporting muscle group for the military press. Since the tricep already gets some fatigure from the pressing, I prefer to do some tricep work on that same workout and give it the next day or two to rest. This is basically the same reason for combining chest day with triceps too. Same concept for Back and Bi's day. Bi's support many back movements so it only makes sense, for me, to combine the two. Most importantly, this split lets me finish my lifting within 50 to 60 min and then I have time for some cardio and can get the hell out of the gym; no more two hour days in the gym for me.

Many people choose to work Tri's and Bi's separately which is totally fine too, just find what works best for you. Some lifting systems will call for Chest / Shoulders to be worked together or even if you have to condense down to a 3 or 4 days split. Bottom line, find something that works for you.

I've included a link to an article that discusses all kinds of splits and benefits of. Enjoy.
http://www.t-nation.com/free_online_article/sports_body_training_performance/ten_killer_splits