Finding time is the most typical objection. You will always have demands on your time from your career, your spouse or partner and even kids if you have them. One of the best ways to overcome this challenge is to schedule your workouts in advance and stick to it. Even if you only have 30 minutes to workout you can still get alot accomplished as long as you push yourself.
You may not see results quick enough, so you become unmotivated or discouraged. We are a microwave society but what you have to realize is you need to get away from the instant gratification mindset. Finally, you may be burnt out. Everyone hits a wall or barrier from time to time, don't let this stress you out to much . If you find this happening, just take a day or two off and re-evaluate your goals.
Like I said before knowledge of different workouts and what seems to be the most effective helping you get the results your after seems to be one of the biggest factors. Personally, I have spent hours of time cutting out different workouts from magazines and pasting them in a journal, this was VERY ineffective. I started looking around the net and found a spot where I could access over 100,000 different workouts from 43 sites all at one source.
This has really to be a great value and has delivered more than what I honestly expected it to. It has given me countless exercises that target "problem areas" and made my workouts more efficient.