Customize KDE appearanceFix unreadable tooltips:
System Settings > Application appearance > Colors > Colors > Color set > Tooltip > change Normal Background and Normal Text colors.Disable blue shadow under active windows:
System settings > Workspace Appearance > Window Decorations > Configure Decoration > Shadows > disable Active Window GlowCustomizable clock and icon-only taskmanager:
install kdeplasma-applets-adjustable-clock and kdeplasma-applets-icontasks then add them to a panel
sudo yaourt -S kdeplasma-applets-adjustable-clockEnable hidden effects
sudo pacman -S kdeplasma-addons-applets-icontasks
By enabling the according effects in System Settings > Desktop Effects > All Effects, these below hidden effects will be activated.
A note about Present Window
effect: beside assigning the effect to corners and edges by going to System Settings > Workspace Behavior > Screen Edges, this can also be used as Window Scaling effect as in Unity when clicking on grouped tasks in the task manager. This requires the icon-only taskmanager above installed. After adding it to a panel, right click on the area where the taskmanager is > Icon-Only Task Manager Settings > Behaviour > Group click action > Present Windows Effect.
Make KDE less resource hungry(my KDE is now only 100MB RAM heavier than Xfce)If you like this how-to, please verify that it is safe to use in your comment.
There are more tips and tricks to come.
This how-to is inspired by this post. My thanks go to its author.
Credits also go to  Step 1:
Configure System Settings to disable animations, desktop search, and many desktop effects. After finishing this step, you will have already saved a lot of RAM and CPU.
In my case, OpenGL gives much better effect transitions. Changing it to XRender MIGHT be good for some graphics cards. Test it out yourself.Step 2:
disable more services to save more RAM.
as root, disable unwanted autostart applications by moving the startup files elsewhere. They can be found in two places/usr/share/autostart/
For example, I created two backup folders and moved unwanted files there/usr/share/autostart/backup/