Here are some commonly used Arc keyboard shortcuts:
New Tab: Control + T
New Window: Control + N
Close Current Tab: Control + W
Show/Hide Sidebar: Control + S
Switch Tabs: Control + Tab
History Forward: Alt + ->
History Backward: Alt + <-
Split Window: Control + Shift + Plus
Close Split Window: Control + Shift + Minus
Switch Focus in Split Window: Control + Shift + 1, Control + Shift + 2, ...
View History: Control + H
Zoom In: Control + Plus
Zoom Out: Control + Minus
Reset Zoom: Control + 0
Reload Page: Control + R
Find in Page: Control + F