I train 5 days a week
Day 1: Shoulders (Delts)
Day 2: Arms (Biceps, Triceps)
Day 3: Legs (Quads, Hamstrings)
Day 4: Back (Traps, General Back)
Day 5: Chest (Pecs)
When training for any sport or for overall fitness, you should always train the whole body as all muscle groups require opposite groups, for example, biceps work with your triceps as opposing muscle groups. Also exercising your legs especially weight training sparks an increase in anabolic hormones which then causes an increase of the whole body. Also I recommended that you do supersets while undergoing weight training at the gym as it hits your muscle groups hard rather than just doing a single exercise and then resting.
For example, if you are really wanting to increase your back size and strength, you will want to work on a compound exercise followed by an isolation exercise, so this will include a Deadlift followed by chin-ups or pull-ups. Wide grip pull-ups will give you the best increase in back size and strength. Also after your first exercise, in this case the Deadlift, make sure you go straight onto the Isolation exercise without rest, rest should be undertaken after the second exercise (Isolation in this case).
Muscular Endurance: 12-18 Reps
Size and Strength: 4-8 Reps
If you don't understand compound or isolation exercises, just search them on google or any exercise website.
Personally I started Trial biking around 2 months ago, so I am still learning the basics.