human nature........ it is often harder psychologically to do the things that you are weaker at

i think that for your goals and what is probably your composition a series of exercises covering all muscle groups would be beneficial for you. this will help increase core strength and general muscle tone.

you shouldnt need a spotter for these exercises, the aim isnt to push heavy weights, it is to work the whole body and stimulate the muscles.

ive knocked up a program of weights below for you. a few elements are key imo,

firstly workout intensity, try and keep the momentum up. keep the sweat up. keep the blood flowing. try not to pause more than 30 seconds between sets which means that if you are changing equipment you need to do it quickly.

secondly focus. try and get a picture of the anatomy and visualize the muscle groups that will be used for each exercise. when you do your exercise concentrate on the contraction, squeeze the muscle, isolate the movement.

thirdly technique. if you are struggling with any weight then drop it. it will save injury and be beneficial in the long run. trty not to compromise technique. in doing this it is helpful (essential imo) to know how each movement / exercise works, which muscle it works and what you shouldnt be doing (for example often when you see people doing biceps curls they swing with their shoulders to jerk the bar up - this is a complete waste of time imo).

anyhow try this out, ive split it into main muscle groups.

Chest
Barbell bench press
1 set x 10 reps
Dumbell Flyes
1 set x 10 reps

Shoulders
Seated Barbell shoulder press
1 set x 10 reps
Lateral dumbell raise
1 set x 10 reps
Front dumbell raise
1 set x 10 reps

Back
Chin up or (cable pull down)
1 set x 10 reps
Barbell bent over row
1 set x 10 reps

Legs
Barbell squats (good core exercise not just legs)
1 set x 10 reps
Barbell lunges
1 set x 10 reps

Arms
Barbell curls
1 set x 10 reps
Triceps extensions
1 set x 10 reps

Abs
2 sets x 20 reps crunches
2 set x 10 reps leg raises

Try and get this all done in half an hour max. I have worked on the assumption that you have access to a set of weights (a cheapo argos set will suffice tbh).

If you dont have access to other sources, this site - http://www.exrx.net/Lists/Directory.html - can be quite helpful in showing you how an exercise is performed.

Good luck