Many start the transition to civilian life within a few short months of the separation date. This places stress on the process, and is unnecessary. There are incredible opportunities for a veteran in the civilian world. One just has to prepare. Employers seek out veterans because they are "vetted". They generally have clear driving records, clear criminal histories, an immense degree of Attention-to-Detail, and responsibility. Employers are constantly dealing with employee theft, lack of commitment, and substandard workmanship. A new veteran is like a breath of fresh air. All we have to do, as employers, is determine if they are serious about a career, or looking for a easy ride after the military.
One should start 2 years before separation, if possible. The first step would be to figure out what makes you happy. You don't stand a chance if you are doing something you hate for eight hours a day. It may be the field you did in the military, or something completely different. Whatever you think it may be, do your homework. Contact civilian establishments that engage in this activity. Volunteer to come in for a couple hours, and be honest. Tell them that you're transitioning, and feel it may be a career choice. Start this no less than 2 years before your separation.
If your selection is the thing you want to do, then find out what the civilians in that field regard as important. It may a certificate, or a course. It may be license of some sort. Find this out, and pursue it before the 12 month mark from separation date. NEVER, EVER, ASSUME! You may believe one field is in demand, or pays top dollar, only to discover it is false. Do this research aggressively, because your happiness depends on your preparation. You may find out early that this career choice isn't what you thought. You still have time to conduct research on a different field. DO NOT let money be the primary motive for a particular career choice. It should play a part, but not the primary one. For the most part, civilians do not have Tax-Free allowances. Income varies greatly. I personally feel that being a QC Inspector for Taco Bell would be the most glorious job on the planet, but may not pay the bills, and may shorten my lifespan dramatically. I found pleasure in Telecom technology. It challenged me, and gave some variety. I compromised. The job I chose required a little desk work, which I didn't care for too much, and some outside work, which I truly enjoy, except during extreme weather conditions. You will also be required to compromise. It may be the location of employment, starting wage, or a job description that may not contain everything you love. If you try to concentrate on the major tasking that you will enjoy doing, then you have succeeded in narrowing down your career choice.
Try to reduce or eliminate financial obligations. The smaller the budget, the greater the range in starting salary you can afford, the less stressful the transition will be.
Do not rule out small businesses. Getting in on the ground floor of a small venture that grows is a great experience. They may not offer the benefits, but do offer the growth potential. Your opinion tends to hold more weight in small businesses. After all, you have spent years solving problems, why not benefit from it.
Remember this, you have earned a gift in the years you have served. You are in demand in the workforce. Do your research to ensure you offer yourself the most positive experience possible. Do not settle for whatever you find. That practice is left for those that do not prepare. Good Luck.