What is the schematic capture/PCB layout design cycle?
Agree on functional operation and performance specifications
Start designing the hard bits first and use a simulator
Make sure parts are available
Go back to (1) if the task is impossible and redo the spec
Start integrating the simulations to ensure different sub-systems of the circuit work together
Go back to (1) if the task is impossible and redo the spec
Start developing the schematic that is your definitive circuit
Choose the rest of the parts and make sure the footprints you have are double-checked or have been successfully used before on previous PCBs
Start designing the PCB and if can't be done in the space available go back to a relevant earlier stage such as (1) or (2)
Complete layout and if you have the tools, and is deemed necessary simulate the effects that might make the circuit layout problematic such as when designing RF stuff.
If PCB has to meet safety creepage and clearance requirements then get it double-checked
Order PCB, order parts, get prototype built
Test it to spec agreed in (1) - this could involve many many tests and there are probably reams of information that could be said here but space and time limits me!
Go back to relevant earlier stage if specifications are not met.
This is usually called Design verification
Create/modify the production documents including a production test spec
For first run of production, ensure Design is validated (extra special care to make sure results are exactly as verification results and if not go back to an earlier stage)


Hopefully, by the time you get to this point you'll have a pretty good design. Your PCB is fundamental to the schematic despite it never appearing on it (well maybe fixing holes etc). The PCB touches every single electronic component in your design - very important to do the job to what was agreed on day 1 (or amended via the process).

I'll also add that this is just off the top of my head and, there are plenty of variations on this such as when designing specifically for an end user - obtaining customer approval at several points along the way is a necessary part of the process and this should be agreed up-front. Also, some products require 3rd party independent testing to "prove" they comply with regulations such as EMC, safety etc..

Between #5 and #6 it is worth mentioning that bread-boarding certain parts of the design may be done where it is felt that the simulation may not give the full picture. This is definitely not uncommon and, designing a PCB just to rigorously test certain parts of a design, is a valid step along the way even though the bread-board/PCB may never get used on the "real" job.

Before #15 you should also start to consider (when production run quantities are not trivial) placing orders for production parts taking into account lead times. You should also be starting to think about any special test fixtures that need to be introduced and doing this in enough time so that the first proper production run is not delayed.