This is a shorter version of the article I published yesterday at linuxgraphics.ru. The sole reason for doing it is that I wrote all these things many times in forums and I ‘d like to refer to one single text in the future. How selfish 
Please note that it implies you are using GIMP 2.3.11 and above.
Here is a visit card of people who use GIMP mostly for taking screenshots:
What do we see there except a geeky (IMHO) Gtk+ theme?
- Font size in GUI is quite large.
- Widgets are quite large.
- Instrument properties palette doesn’t fit the window horizontally.
- Default set of dialogs has, IMHO, both useful and not so useful dialogs.
This is what GIMP suggest users by default and what they often complain about. Could this be improved? Definitely yes, let’s have a look, how exactly.
Fonts and widget size
GIMP uses its own Gtk+ themes for ages. Usually you can choose between Default theme and Small theme. Currently most noticeable difference between them is taking place thanks to reducing font size, which makes checkboxes and buttons smaller, because they automatically adjust to length of text. Besides, Small theme uses smaller icons for toolbox window (16×16 instead of 22×22).
To switch a theme open Preferences dialog, go to Theme tab, click on “Small”, then “OK”. Changes will apply immediately.
That’s not all. Remember about font size? Have a look at /usr/share/gimp/2.0/themes/Small/gtkrc file. It has such a string:
# font_name = "sans 8"
Now copy /usr/share/gimp/2.0/themes/Small to ~/.gimp-2.3/themes/ and rename it to, say, “even smaller”. Now you can pick your favourite text editor and adjust ~/.gimp-2.3/themes/even smaller/gtkrc like this:
font_name = "Tahoma 7"
This will make GIMP using Tahoma 7pt font for all widgets that contain text and dialogs, therefore, will become smaller.
Further optimization is possible by tweaking gtkrc. You might like read documentation on Gtk+ for that.
Width of dialogs
You might like disabling Help button to get narrower dialog windows. Some dialogs have several buttons in the bottom row, and if at least one of the buttons has a long caption, all other buttons will have same width. Thus getting rid of one of the buttons you don’t use regularly, might be a good idea, and Help is a good candidate. You can do it in Help system part of Preferences dialog. Here is before:
Here is after:
You can still open context help by hitting F1 (can be disabled as well in the part of Preferences dialog).
Layout optimization by redocking
You can redock any floating dialog and start a new group of docked dialogs easily. For reference please read appropriate part of GIMP docs.
Layout is a very objective thing. A set of dialogs a user might need varies from person to person. However, if you do a lot of photo retouching, I suggest keeping Layers dialog and Instrument Properties dialog opened simultaneously (therefore in different docked groups) and add the Histogram dialog to the top or the bottom of one of them. Note that you can switch between many dialogs using default hotkeys. Here is my usual layout:
Preview size
By default GIMP uses quite large (again, IMHO) preview areas for Layers, Channels and Undo History dialogs.
Adjusting Layers and Channels dialogs is a piece of cake. Just like any other dialog they have a context menu, and in these particular cases you can find there a submenu Preview size, where you can pick a size that will suit you. I for my part went for tiny, because when I do retouching, I use text for reference, not previews. Sure, if you are blessed to use 21’’ Lacie and you use preview for reference, you can go for Gigantic (saw it a couple of times in tutorials by Bernhard “devvv” Stockmann from gimpusers.de — great information resource in German, by the way). Here is tiny:
Here is gigantic:
You can do the same in Interface part of the Preferences dialog.
It’s not same easy regarding Undo History dialog. Sven reported that it’s difficult to recalculate previews of actions on-fly, so you are doomed to use text editor again Open ~/.gimp-2.3/gimprc and add the following:
(undo-preview-size large)
Large is the default value used by GIMP. You need to change it to one of the following values: tiny, extra-small, small, medium, extra-large, huge, enormous or gigantic. You need to restart GIMP (if running) to let changes apply. Here is what you will see with tiny:
Normal and fullscreen modes
Fullscreen mode in GIMP is considered as mode for editing by default, since it has all the same settings the normal mode has, including color of background. It’s up to you whether it suits you. I know many users who want fullscreen mode to be preview mode by default. If you are one of them, go to Preferences dialog and Image windows→Appearance. Here you can change default settings. For instance, scrollbars that are enabled by default are of no use, since you have much better ways to navigate a large image (see below).
As for guides and grid, again, it’s up to you whether top leave them or to disable them by default. For me they are disabled, and to enable them I’ve setup two hotkeys taken from Inkscape: “|” for guides and “#” for grid (I use them in Scribus too). If you are migrating from Photoshop, you might like set Ctrl+; and Ctrl+��? instead — just enable dynamic hotkeys in Interface tab of Preferences dialog and go through View menu, pressing hotkeys you want for each menu element.
Image navigation
This is rather user experience, not UI, related. One thing you might immediately like in upcoming 2.3.12 is using Spacebar for panning by default. You can still revert this behaviour to the previous in Image windows tab of Preferences dialog, if you prefer to switch to Move tool and not to Panning.
There are other ways to navigate images you might like to use:
- Dragging with middle mouse button.
- Combination of Shift + arrow keys.
- Small navigation widget in right lower corner of image window.
- Navigation dialog.
- Using bottom and right part of touchpads (for laptop users).
I hope that was helpful for ya!