Two common methods of grounding.
Common ground can be broken out as two types. (simplified)
Both are known as GROUND.
In most cases you will probably use something similar to the post from Perry
However if you are planning a CNC, multiple motors, servos, actuators etc. type of project there is another method to consider.
STAR GROUNDING
In its most simplistic it is a central point where all grounds meet using a "star" formation.
Often also used in audio, musical instrument situations to name just two.
The star ground is a single reference that connects both analog and digital ground planes.
This is to help eliminate ground loops.
A ground loop (simplified) is a dual route to ground that can cause signals to interfere with each other.
They can often be awkward to diagnose and in some cases fix.
Electrically there can be multiple differences in the way both schemes work even though it may on the surface look like the grounds are all just connected to each other.
Simple GROUND tips.
- Try to keep ground and signal leads as short as you can.
- The current return paths must also be kept short (aka ground).
- Long wires can pick up noise and should be kept as short as possible or shielded.
- Any grounds that present high frequency signals should not be shared with other more sensitive grounds.
- Try to avoid introducing inductance with coiled wires or similar although twisted pairs are a basic loop
- Better to avoid ground loops that can be a source of interference into your ground or transmission of your signals to other parts of the circuit.
Other aspects to be considered but not dealt with here are :-
- Ground Planes.
- Grounding Rods.
- Chassis Ground.
- Ground Bonding
- Earth Ground.
And a few more but for the purposes of keeping it simple I only added the above to compliment Perry's post.
Also my thanks to Robin and Perry for the insights and assistance.