List your specific goals and chose a role model.
If you are looking to lose bodyfat, then you are going to want to focus a lot of your workout program on cardio. If you are looking to gain muscle size, then it makes sense to spend a large percentage of your workout program focusing on lifting weights. I think it helps to find a role model. My personal role model is Brad Pitt in Fight Club. In that movie he is very lean and compact. I have developed my workout program in a way that maximizes fat loss, so 75% of my workout is on cardio and 25% lifting weights. This workout program allows me to maintain a very lean look year round.
Decide how much time you are going to devote to exercise.
In designing your workout routine, you are going to have to figure out how many days you will be able to workout. Contrary to popular opinion, I think you do need to workout 4-5 days minimum to achieve great results. Many personal trainers have their clients perform workout programs 3 days per week. The body was meant to get daily exercise. The people in the best shape I know perform at least some exercise every day. If you have 7-8 total hours to devote to exercise, you will get better results spreading those 8 hours over 6-7 days -vs.- having three 2-hour workouts. As an example… Matthew McConaughey simply tries to work up a sweat for at least one hour every day. That is a simple technique that obviously gets great results.
Pick exercises that are right for you.
What I typically see is the trainer taking every person through the exact same routine, regardless of their body type. I also have head people complaining that a certain exercise hurts them. The problem is that the personal trainer simply can’t get into your head and know what the exercise feels like to you. For instance, I have a spinal injury so I have to avoid any type of crunch exercise in my workout program. Only you know how a certain exercise feels to you. I use a lot of dumbbells in my workout program, since I can really feel them working my muscle. If I was a personal trainer I would probably design workout programs for my clients using dumbbell exercises. This would be a big mistake, since many people get a better workout using barbells or machines.
Educate yourself about fitness.
My advice is to educate yourself using the Internet and then come up with your own workout program that is perfect for you. Not only will you experience greater results, you will save time and money getting to your goals. There are several great resources online which will help you create your ideal body. Finding a really good e-book will cost less than the price of one session with a personal trainer. In no time flat you can easily design a solid workout program and fine tune it over time.