Brienne's actually written a pretty great article on this, here: http://agentyduck.blogspot.com/2014/12/how-to-train-noticing.html I can't seem to find the article, but she has another one where she talks about using an old style ticker for positive habits. She clicks it every time she notices, and it's not only immediate feedback, but it gives you a running tally of how many you've done for the day, which is a bit gameified.

If it's a negative habit you're noticing, an old NLP standby is to snap a rubber band on your wrist, just enough that it stings.. A more modern version of this is the Pavlock wristband - it shocks you when you do the negative thing.

Another good one is to wear a bracelet, which you switch from wrist to wrist when you notice the habit. I believe this originated with Will Bowen and his no complaint experiment. These remind you throughout the day by having the wrist band, and every time you switch it, you'll be paying more attention because you haven't habituated to the wristband yet.

Finally, there's apps like tagtime/moodrecorder/etc. These are installed on your phone and pop up variably throughout the day, asking you to be present to internal state and record it. This gives you a more holistic view of what's going on internally throughout the day.