When the river is deep, it's easy to get wet. (Economic prosperity)
We're scraping polish off our boots for soup (= times are tough)
He has stones in his field (= he has a hard row to hoe)
Gave like a six-teat cow (= sang like a canary)
We’ll cut down that tree when it’s grown (= cross that bridge when we come to it)
The redfinch complaining of the chaffinch (= pot calling the kettle black)
Herding finches (= herding cats)
No dancing killed the ant (= all work and no play makes Jack a dull boy; from a children's fable)
We've started out with our harness tangled (= got off on the wrong foot)
Don't make a scarecrow and stand in your own field (= don't keep a dog and bark for yourself)
More holes than a moth's lunch
As drunk as a dockworker
Three-days-fruit (= drunk, possibly as a dockworker)
Too swamped to be bothered bailing (= three-days-fruit; an Islands expression)
Take to something like gnomes to mushrooms (= a duck to water)
That apple's already off the tree (= that ship has sailed)
You build the house you're paid for (= he who pays the piper calls the tune)
A carnival of fools (= a (metaphorical) circus, a Mickey Mouse outfit)
I'll push him down one well and fish him up another (= I'll kick his ass)
Catch the fish that's biting (= strike while the iron's hot)
Working like a gnome (= working very hard; some, though by no means all, gnomes consider this expression offensive, as if hard work defines them)
Like selling gritty melons (= a tough sell)
A pipe with two ends (= a double-edged sword)
Water in front and fire behind (= the carrot and the stick)
Out of the mud and into the quicksand (= out of the frying pan into the fire)
Knows where the meat is in the stew (= knows which side his bread's buttered on; has an eye to the main chance)
New bread on an old plate (= an appropriate innovation which preserves important aspects of tradition)
In someone's happy basket (= in their good books)
Holding in a bit of one's breath (= anticipating something)

Conventional expressions:
My pleasure to give (a response to thanks, like "you're welcome")

Gnome sayings:
You're talking tonnage to the production foreman (= you're preaching to the choir)
We're two pumps for three (= we're extremely busy)
I can't scratch a glyph on it (= can't put my finger on it)
We're starting with our tools already forged (= we're making assumptions)
Innocent as a moth (= completely without guile)
Like eating mushrooms (= very easy; like falling off a log)
Talk about the pit in the floor (= the elephant in the room)
He'd chew bolts and spit out filings (= he'd be very angry)
We'll need to chase down every tunnel (= pursue every avenue)
In the middle of the cavern surrounded by lights (= under a lot of scrutiny)
More to him than sticks above ground (= he has hidden depths)
He'll throw a cam-belt (= he'll be very upset)
May props and stays hold hard and preserve us all (= angels and ministers of grace defend us)
We'll clear that rubble when it falls off the ceiling (= cross that bridge when we come to it)

The Three Daughters of Mathematics according to the elves: music, magic, astronomy

The Red General:
If you're in a battle you can't win, find the battle you can win.
Chaos favors the prepared

Berry's old shaman:
The happy person doesn't seek the shaman