1 – Don't wait for it.
Motivation ebbs and flows with experienced lifters just as it does with inexperienced ones. The difference is, the experienced lifter allows herself to feel unmotivated and shows up at the gym anyway. So stop analyzing your feelings about working out and just go.
Don't train because you're motivated; train to become motivated. Unless you're preparing for a competition, you probably won't feel fired-up on a daily basis. So show up, put in the effort, and find your motivation in the middle of the set. It'll be there waiting for you... unless you are completely physically burnt out. And that likely will only happen if you're an advanced athlete who trains constantly or is ill.
2 – Envision the work.
Think about the physical feeling of training. Put your mind on the work. Remember what the bar feels like in your hands and what your body feels like moving it. Thinking about training will make you want to go back, and it doesn't really matter what your main goal is.
Trying to get jacked? Think about what the mind-muscle connection feels like, and what you'd be doing to achieve it. Remember what it feels like to get that skin-bursting pump.
Trying to get stronger? Think about what it feels like to lock out during a heavy set. Picture that moment.
Trying to lose fat? Think about how it feels to push through a challenging interval, metcon session, or whatever else you've been using.
Trying to perfect your clean? Think about what it's like to be in the correct positions from the floor to the extension to the catch.
Some people don't even realize they do this. When I was a kid, my big brother would always walk through the living room and stop briefly to work on his forehand, or backhand, or serve. He was constantly honing his tennis skills and putting his mind on the court when his body wasn't there.
People who love the work can't stop thinking about it. They practice the movements when they think nobody's watching. Their thoughts reinforce their behavior and their behavior reinforces their thoughts. My brother never needed other people to motivate him to go practice, and because of that, he was the best.
3 – Avoid regret.
"I don't feel like working out today, but I'll regret it if I don't." Ever hear someone say this? I said it this morning. It got me in the weight room.
If you're not stoked about lifting, remember that the blah feeling you have in the gym parking lot is short-lived. But if you blow off your workout, you'll regret it the rest of the day, or later in the week when you need to make up for what you missed.
Even if you actually WOULDN'T regret missing it, convince yourself that you would so that you're compelled enough to start. Sometimes starting a workout is the hardest part. So whenever you say you don't feel like working out, follow it up with the reason why you will anyway.
Although motivation isn't necessary to get stuff done, it's nice to have. The good news is, getting yourself fired-up is a skill you can learn. Self-motivated people aren't the ones who say they "don't need motivation." The self-motivated are the ones who find the silver lining and enjoyment in any behavior they're wanting to adopt.
They can also find the drawbacks that come from NOT doing what they want to make habitual... that's where this avoiding-regret trick comes in.