The most common and most likely answer to this crossword clue is the 5 letter word CLICK
I've seen this crossword clue in The Sunday Telegraph
C
L
I
C
K
Buddy explains!

The straight part
We know that "Get on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case get on = click.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CLICK mean?
CLICK noun- A brief, sharp, not particularly loud, relatively high-pitched sound produced by the impact of something small and hard against something hard, such as by the operation of a switch, a lock or a latch, or a finger pressed against the thumb and then released to strike the hand.
- An ingressive sound made by coarticulating a velar or uvular closure with another closure.
- Sound made by a dolphin.
- The act of operating a switch, etc., so that it clicks.
- The act of pressing a button on a computer mouse, both as a physical act and a reaction in the software.
- A pawl or similar catch.
- To cause to make a click; to operate (a switch, etc) so that it makes a click.
- To press and release (a button on a computer mouse).
- To select a software item using, usually, but not always, the pressing of a mouse button.
- To visit a web site.
- To navigate by clicking a mouse button.
- To emit a click.
- To make sense suddenly.
- To get on well.
- To tick.
- To take (a photograph) with a camera.
- The sound of a click.
- A brief, sharp, not particularly loud, relatively high-pitched sound produced by the impact of something small and hard against something hard, such as by the operation of a switch, a lock or a latch, or a finger pressed against the thumb and then released to strike the hand.
- An ingressive sound made by coarticulating a velar or uvular closure with another closure.
- Sound made by a dolphin.
- The act of operating a switch, etc., so that it clicks.
- The act of pressing a button on a computer mouse, both as a physical act and a reaction in the software.
- A pawl or similar catch.
- A detent, pawl, or ratchet, such as that which catches the cogs of a ratchet wheel to prevent backward motion.
- The latch of a door.
- A kilometer.
- (usually in the plural) Kilometres per hour.
- A detent, pawl, or ratchet, such as that which catches the cogs of a ratchet wheel to prevent backward motion.
- The latch of a door.
- To snatch.