One guideline for going up in weight is to continue with the same weight you have, until you can do two more reps than usual for two workouts (this is when you're working out in a gym, and go for a range of reps.) On workouts like Cathe's, where we don't do a rep range (but could change them to be so, by doing the 12-rep workouts starting at 10 reps, then moving), you'll have to use another guideline. When reps get easy and you feel you could do more (the last two of a set aren't a challenge any more), then increase weights.
Generally, going up 5% for smaller muscle groups and 10% for larger muscle groups is a good guideline, though it might be tough (especially that 5%) depending on what weight increments you have available.
"Tone" is just a word commercials use to promote weight routines to women who fear the words "build muscle." Unless you are genetically apt to build more muscle (a mesomorph, short/stocky stature, or more testosterone) you won't "bulk" from lifting weights. And if you start to feel you are, you can easily cut back on weights, go to a higher rep program, or do more cardio.
Growing muscles takes effort, as well as adding more calories to your diet to gain (muscle) weight.
