Well, I can tell based off what you typed that you don't know
much about the difference between slim and tone.
I'll describe it in the simplest of terms.
If you want to be "tone" you have to build muscle while having
very little body fat. Thus, to the point where the muscle fibers
fairly show on your body.
If you want "slim" arms you must simply have little body fat.
I'm not going to assume you're over weight but a little bit more information
about you would help us as well. So I'm just going to assume you are in
a pretty descent shape, but you don't have slim arms.
You CAN NOT
spot reduce fat anywhere on your body.
This is just a completely known fact.
Your body chooses where it will lose fat.
By doing a bunch of random arm exercises won't
make your arms any smaller.
way to achieve a slim figure is to diet and exercise.
If you are trying to cut fat, then you should be on a diet
and performing a lot of cardio.
I'll even help you where to begin your planning for dieting and work outs.
Go here to choose a fat loss training program.
And here for a beginners guide to fat loss. (Which is something I believe everyone
should learn regardless if they train or not)
I recommend everyone to this site,
simply because it has all you need to know.
I've done all I can. Its up to you now to decide if you willing to learn
and give it all you got to get to your goal.