A couple of the things I like to do and use to remind me to scout.

Early-game:

• Scout at 9th, or even 8th on 4 player maps when you suspect a cheesy opponent.
• Scout at 9th or 10th on 4 or 2 player maps when you suspect aggressive play style.
• No matter what!: Scout at 12th by standard definition.

I like to think of the "standard" as being the proper use for the 12th drone, as it is the first round of droning to come with a simultaneous spawn [of another drone] to occur.

-First 2 pairs of zerglings on the field = Xel'Naga towers and ramp duty. (Ramp being priority, followed by both being highest priorities)

To set my self up for mid-game scouting, in the early game [also a note on my hot keys] I like to use my starting overlord as a Scout (face-palm) on hokey "2," my 2nd overlord as a scout, on hot key "3" going the opposite direction of my starting overlord, or to either my natural or their natural expansion if playing on a two player map. And, hot key "1" as my drone scout to quickly spam through 1-2-3 and pick up information or maneuver my drone. Point being, in conjunction with drone scouting once I find my opponent I flank their base with my overlords. In preference, at a point-of-view where I can glimpse gas timings and base choke points, or just beyond sight of such a feature. Also, until my scouts are killed they always have preference over army hot keys in terms of "reach-ability" therefore, 1 is most typically my active scout, followed by army hot keys unless I'm in expectation of a micro-intensive situation in which case I tend to slice my army into either groups of 3 of 4 as roughly as evenly as situationaly possible, for flanks/surrounds/counters, camera maneuvers etc...

Mid-game:

• Using my overlord setup as just mentioned, in typical fashion will both become overseers' once I get Lair slash have enough gas to limp them into the game depending on how greedy or pressured I am.
• Either from the speed of overseers' outright or their changelings provide fantastic scouting.

Late-game: Remind my self that if I properly apply my principles of scouting and the information received I should have won already, then: Scout.

Last thought: One other thing I do to remind my self to view the mini map [with more mention of hot keys] is limit my "ball army" hot key to a number greater than my number of hatcheries [queens' assigned to them specifically] starting at key 5 for my main etc...whenever possible, thereby leaving my "easy" hot keys for macro and scouting; essentially forcing myself to watch the map to track army movements other-than-scouting, and keeping my focus on where the bulk of my adjustments need to be made.

Hot key order being:

• 1 Drone Scout > Primary scout (changes most often)

• 2 Overlord > Overseer (one of 2 that open for situational hot keys)

• 3 Overlord > Overseer (two of 2 that open for situational hot keys)

• 4 Hatcheries en mass

• 5-9 Queens'

Hotkeys

One of the things I could never just bring my self to do was, use "Screen Locations" and the hither to "Jump to Screen Location" hotkeys being something like Shift+F5 to set location 1 which was jumped to by pressing F2..etc..whatever; So instead, noticing how well it CAN improve your micro & scouting is use (tilde) and CAPS LOCK as Screen Locations, and Shift+ (tilde), Shift+CAPS LOCK to set those locations. This one change alone moved my base management from excellent on 3 bases, to excellent on 5 bases; because it essentially frees up your 8, 9, 0 hotkeys do be...whatever and allows you to jump directly to your Main & Natural hatcheries to inject using ` + CAPS LOCK, giving your 5+6+7 hotkeys (mine are queens) a role into the late game where ideally I want to have 5 bases minimum.

Remember, to always have an anticipation of what your opponent wants to do--and prepare (read: get larva, and required tech structures) suitable responses to their tech structures, bearing in mind gas directly indicates how tech "heavy" the play will be vs how macro-orientated it will be with quantity over quality. Other than that to improve on any scouting, you have to do it, and feel the results of it.