for lifting weights i can tell you my plan, and lots of people follow the same type of plan.
basically i work out 4 days a week, and i never work the same body part more than once a week. except for calves and abs, they can be worked every other day.
you said you want to focus on your arms and abs, that's good, but don't neglect the rest of your body. All of your muscles support your bone structure and neglecting any of them could lead to posture problems at the least.
i go to the gym on monday, tuesday, wednesday i take off, then back for thursday and friday.
i work every body part in those 4 days.
monday = chest only
tuesday = back and legs
thursday = biceps and triceps
friday = shoulders
this gives each of those muscle groups lots of time to recover before they get worked again. (muscles grow through a repetitive cycle of destroying and rebuild)
Also, only working one body part makes for a quick weight-lifting session, and leaves me lots of time for cardio. (i usually do 30 minutes every time i'm in the gym, on either the bike, treadmill, stair machine, or cross country trainer)
When I do the weight lifting exercises i usually follow the following routine.
Do about 4 movements per body part.
Do 3 - 4 sets for each of these movements
Do 8 - 10 Repetitions per set.
The first set of the day, i usually take a really light weight to get my muscles used to the upcoming activity, and then i progressively build up to my maximum in the last set for the exercise. I try not to over do it however, keeping in mind that I still have 3 other movements that are going to concentrate on the same body part. I don't want to over do the first movement and not leave myself strength to get through the rest of the movements.
As you get towards the end of your workout, you can begin to push yourself a little so that you get the maximum benefit for that muscle group.
I also tend to have anywhere from 6 to 10 movements for the same body part, and even though i only do 4, i try and do 4 different ones every time i work that group. That way, you never give your body time to get used to the workout and so that helps you get maximum benefits to your muscles.
Some people don't have time to get into the gym that often, and so they prefer to work multiple muscle groups per session. I don't have a routine set out for this, but what I have heard as a strategy for this type of workout is to start with the movements that work the muscles closer to your spine, and then work out from there.
ie, if you do chest and triceps in the same day, do chest first, and then move on to triceps.
I think i'll stop blabbing now.
ps, dont' listen to what pr0nstar said about working the same muscle every 48 hours, at the least you should give them 3 days to rest.