Personally, I'm coming back from an injury that sidelined me from my normal workout routine for several months. I worked hard prior to injury to work my way up to five-day-a-week workouts and conditioning my mind to understanding that workouts were a non-negotiable habit.
Trying to re-establish a workout routine after being cleared from my physicians was like pulling my own teeth. Gritty, really unpleasant, and frankly, crazy. The attempt to start a new habit is so maddening because it's often ourselves vs. ourselves in a battle of good vs. evil.
One tip I've discovered recently is that of continual improvement. Instead of going from 0-to-60, we go from 0-to-10-to-20... and so on. A similar you may have heard of is kaizen, a process first started in Japanese manufacturing to create great momentum by implementing gradual changes. The continuous improvement still leads you in the right direction, without creating a huge disruption in existing flow.
In our fitness habit example, you can start by committing to 1 workout for the week. Carving out 45-60 minutes out of an entire week is much less daunting than carving out that much time per day. The momentum you feel from that 1 workout will likely move you to another workout, and you'll soon be up to 3 times per week... and t model hen more if desired. It's amazing how quickly the excuses seem to dissipate when you don't leap for the moon on the first attempt.