You've got two choices as far as fitness goes this year...
Choice 1: Known as the warrior method: be sensible about what you eat, make it to your workouts, and ride the momentum through the year.
Choice 2: Also known as the "screw it all" method and entails using the time between all the holidays and WEAKends to establish a new personal best for increased sluggishness and body fat (on average people put on around 10 lbs between November and December, yikes!).
For about 3 weeks in January, "choice 2" people flood gyms across the country wearing new gear with fancy new Ipods (with the best playlists) thinking it will motivate them into sticking with their program for the long-term (funny). Then they limp out to the parking lot in their new wacky toe shoes and join the witness protection program. I see this all the time.
There is no blanket solution...
You can however figure out the answers on your own if you ask yourself the right questions. If you are on the fence about sticking or starting with your fitness plan, think about why you want to do it and make a conscious decision about whether those reasons outweigh ANY excuses.
If you have completely fallen off the horse, devise a comeback plan that starts you off at a level where you can maintain some consistency. Nobody cares how much you could squat or bench or how far you could run this time last year and neither should you. Having a sense of humility when you are planning/preparing your workouts will go a long way toward avoiding injuries (which is also a good motivator to keep you on your plan).
Skip turning to a fitness trainer for motivation to get you to show up. If you need to pay someone to talk to you into working out, you need to seriously reconsider your priorities. You need more than a cheerleader. You need to start asking yourself the right questions. That's all it takes.
Create specific deadlines. Goals are dreams with deadlines. Parkinson's Law states that the perceived complexity of a task expands to fill the time you allot it. This means that if you set hard time limits, you are going to be forced to be productive if you want desired results. Estimate how long it should take to achieve a goal and force yourself to finish it in that time frame. Do keep in mind you should be somewhat flexible on your timelines (none of us can control everything out there). Read The Tortoise and The Hare.
Get the hard stuff done first. Everything else will seem easier if you do the hard stuff first. People tend to start the week (or workout) strong with exercises they like and fizzle at the end when, say they get to leg training. As a result, the legs always lag. You need balance in your training plan. Maybe make a list of all the exercises you hate and perform them early in the week. Save your favorites for the end. This is called front loading your training program.
Keep in mind full body workouts will do wonders for your vigor, metabolic rate, and body composition.
Figure out the YOU plan: The best way to discover what eating style works for you is to experiment with periods of elimination. One month, go vegan, another month, try lower dairy. This is known as food cycling. Pretty soon, you will figure out what you need to do to make the fastest progress, and you will develop your own plan to follow for the rest of your life. Be mindful though about just cutting calories. Your eating style needs to match your training schedule. Seek help to address your specific calorie needs so you manage to get all the necessary nutrients in to push you mission forward.