When they say to modify your routine after 30 or 60 days.....
Does it count to just do the same wl exercises but increase the weight back up to a really challenging level? Or should you try entirely new exercises as well? Such as moving from a tricep kickback to a bench dip?
I'd raise your weights as soon as you get to the point that you can comfortably complete however many reps you were aiming for- don't wait 60-90 days! Change the exercises that you do every couple of weeks- or every couple of workouts.
I change up workouts and the amount I lift almost every 2nd workout, I get bored easily... Since I do a 3 or 4 day split I may do the same workout only 2 weeks in a row...
I must get bored really easily because I never do the same workout twice in a row. I'll use different equipment (DBs instead of a BB, for example), different exercises, different rep schemes, supersets - anything that I can think of to make it different. My only exception to the rule is pushups and pullups and that's because I'm on a personal challenge to increase them week-to-week.
I second what Mel said about the weight - it should ALWAYS be 'really challenging'!
OK, I'm another one with "workout ADHD". Other than working on particular goals (bench pressing until I killed my forearms, and always some version of push-ups and pull-ups), I don't think I've ever done the same workout twice, the same way, either.
Well, it gives me hope that maybe one day I will be so creative. But for now, when I'm at the phase where I'm following along in a guidebook for everything I do, I'm not winging it yet. I guess it's like cooking, you have to follow the recipes step by step until they become second nature and then you can do them from memory and modify. I look forward to that day of switch ups!
I'm with you Fran. Although I do change my routines regularly, that process still involves sitting down with several books, printouts, etc. and planning, then writing in my little notebook. I religiously keep track of what weight I'm using to do which exercise, and the sets/reps. The day-to-day variety, if any , consists of changing the order of the exercises I do for a particular body part. I like your cooking analogy though - it's how I learned to cook, and drive DH nuts because I seldom use a recipe as written, but use them more for spice/ingredient combinations unless it's a new ethnic one.
There's been a couple of studies that have shown that your muscles adapt to the rep and set range sooner than they do to the actual exercise.
the concept of undulating periodization is based on this. you basically use the same exercises in the same order workout to workout, but change the rep and set range each workout.
example, you're going to do a full body workout 3 days a week. on the first workout of the week, you'd do 4 sets of 8 reps, the second workout of the week, you'd keep the exact same exercises in the same order and do 5 sets by 5 reps, and the last workout of the week, using the same exercises do 2 sets of 15 reps.
you'll be using a different size weight than you were from the workout before (ie a heavier weight on the 2nd workout than on the 1st or 3rd).
and as has already been mentioned, you need to bump up the amount of weight you're doing each respective workout when you find that the current weight that you're using is not challenging anymore for that set and rep range.
When they say to modify your routine after 30 or 60 days.....
I'll use different equipment (DBs instead of a BB, for example), different exercises, different rep schemes, supersets - anything that I can think of to make it different. My only exception to the rule is pushups and pullups and that's because I'm on a personal challenge to increase them week-to-week. 
