Optimization Guidelines

Hi everyone,
First things first: I'm new to MonkeyC, but on good terms with java and been writing for Android + Wear for some time so presumably I know the drill.
Decided to design my own full screen data field and made it run nice on simulator, but when I install it on my Forerunner 230, data field seems to lack performance during actual usage: at least timer field, which I render as two to three
separate strings depending on elapsed time value is rather quirky and most of the time seconds jump around as if there's a half-second delay, then field is redrawn several times in quick succession to make sure data is actual.

I understand that global questions like "why my code runs slow" cannot be answered, thus I ask another vague one: are there specific optimization guidelines/best practices similar to Android Wear ones such as "always prefer object property usage over variable declaration", "clearing dc every onUpdate takes much processing time" etc?

Right now my prime suspects are full screen actions like dc.clear and dc.fillRectangle, but who knows.
If someone is willing to check my code (a little bit cut to fit message limit), then it is provided below.
Sorry for the large plain text, but emulator reports increased memory footprint if I declare a lot of functions.