'Tone' is often misused when it comes to defining muscles. Here's what I have gathered from reading endlessly on the subject: you can only increase the size of your muscle cells, you cannot not increase the density (number of cells): this is set in stone and based on genetics. So changing your muscle size and body fat are only things you can do to alter the appearance of muscle. With that in mind, if you are weightlifting for solely cosmetic purposes then you are better off just doing a hypertrophy (10+ sets at 12 reps max once a week per muscle group) routine and cutting calories from your diet if you are fat.
But here's the thing:
During sarcoplasmic hypertrophy, the
volume of sarcoplasmic fluid in the
muscle cell increases with no
accompanying increase in muscular
strength. During myofibrillar
hypertrophy, actin and myosin
contractile proteins increase in
number and add to muscular strength as
well as a small increase in the size
of the muscle.
From Wikipedia: Muscle hypertropy.
Basically what it is saying is there are 2 ways to lift: the bodybuilding way or the strength training way.
Now for my real opinion on the matter: don't be the former type of lifter. It's shameful and a result of the Great Emasculation of the late 20th and early 21st Century. Anyone building mass or worried about 'toning' is what I call a "glamor-puss": these are the gym rats who do lots of bicep curls and bench press (and typically use steroids or HGH) yet completely ignore exercises like the clean and jerk, squat, or dead lift.
Get back to the basics. Do the compound man-ercises like squatting, dead lifts, and work up to doing clean and jerks/clean and presses. Also, if you aren't a fatty lifter (which is only slightly better than being a glamor-puss) work on handstand push ups and one armed chin ups/pull ups. Try never to do more than 6 reps or you are getting into the realm of useless muscle mass.
Think about this: the world record for clean and jerk for a guy weighing about 125 pounds in 369 pounds! Can you even dead lift that? Imagine that you are training for ninja warrior and not for getting on the cover of Men's Health (aka Mangina Monologues).
I too was once lost, but have since found my way and now I feel more like a true man than ever before.