Xfce customization, less obvious

We are dealing with Xubuntu here

- Moving things on panels. Right-click on item, pick 'move'. Obvious, yes – but what wasn't so obvious to me, is how items align and stay in groups. There are invisible separators on panels, and you can add more or delete them, according to need. Easiest way to find default ones is: Right-click a panel, open 'panel/panel preferences/items. All things on panel are listed there, also separators – double-click and change 'transparent' to something else. And now you can see it on panel. 'Expand' means that separator pushes items away on both sides. That is, separator in center of panel makes items go to both ends. Do experiment, it's frustratingly educational.

- Xfce menu lacks 'lock screen' option. If needed, it's easy to create: Open your menu editor and add new item to right place, name it, and add exec command: xflock4. Pick an icon. Save, done.
- Xfce has such a nice thing as mime editor (in Settings). Means, you can make certain apps to handle certain files (can't change system defaults, though). If some file is opened in freaky way – like jpg with Firefox, and you can't find jpg at all in mime editor – then open this jpg with app you want to be default. Entry should now appear to mime list. Double-clicking on entry opens edit. There might be occasional need to fix entries which point to app that you removed (but mime didn't notice that). Or something...
- Xfce can have only one wallpaper over all workspaces. Compiz and KDE, for example, can have different ones. There is app called 'wallpaperoz', it has to be downloaded from web and manually installed. This app enables different wallpapers, and also changes them as frequently as you want. BUT, it's slow and lagging when you change workspaces. So, I tried it and I removed it.
- Docks. I am not sure what for they are good – as Xfce lets you make several freely customizable panels and fill them with launchers, drawers, widgets and whatnot. But anyway – there you have some names for googling: Plank dock (simple), AWN (it's not developed anymore), and most famous currently – Cairo dock (looks very pimpy and mac-ish).
- Themes and icons. Next post will be about this. Here I say only - well, obvious: for a simple tuning, look into 'Appearance', 'Window manager' and 'Window manager tweaks' and play around.

Configuration editors: There are occasions when some settings need to be tweaked manually. For that there are configuration editors. If in need or simply curious, take a look. Proper caution should be exercised, clicking like a blind moron is not advisable!
Xfce has a package 'xfce4-settings' which contains xfce4-settings-editor.
Gnome-specific settings come through gconf-editor, Linux Mint uses dconf-editor. Mate desktop one is called mateconf-editor. And so on. Depending on distro, an editor might be already installed – or not.

Tweaking of Grub2 - Not recommended without extensive pre-research!
For serious tweaking DO READ tutorials before, experimenting with bootloader IS dangerous!
One overview is here... googling 'tweaking grub2' gives a lot more.
Here are three less risky things (provided that no errors are made):
- Some easily changeable (and commented) parameters (wait-time before booting OS, for one) are in file /etc/default/grub
- To remove memtest entry from boot menu (if it is there). There is file /etc/grub.d/20_memtest86+
Go there and simply make this file non-executable, in terminal:
sudo chmod -x 20_memtest86+
- If using Ubuntu there are 'Advanced options' entries in boot menu. Those folders contain entries to boot older kernels. If your new updated one works (reboot is mandatory, so you will know if it works) then there is no especial need to keep those older kernels (they take disk space too).
Check which is your last, working one. Type in terminal: uname -r
and you get number of current version. Rev up your Synaptic and find all 'linux-image' and 'linux-header' packages. 'Completely remove' those that are OLDER than your current one (lesser ver number). Be very careful NOT to remove the newest ones. And after all that, type in terminal:  
update-grub
Done.