I had flickering headlights and flickering dash illumination separately,
about a year apart. So it is possible you have two problems, but not
necessarily.

Starting with the easiest thing first, I would suggest the following (mostly
as already suggested by self and others):

1. Lighting Switch - pop from dash, remove and replace the connector at the
back; squirt of electical contact cleaner.
2. Dimmer Switch - pop from dash, remove and replace the connector at the
back; squirt of electical contact cleaner.
3. Instrument pod - remove dash lid, then pull and replace all three/four(?)
connectors. Take the opportunity to replace any blown instrument
illumination lamps while you are there.
4. Headlamps - ensure wire clips are in good shape and properly fitted;
remove units to bench if necessary.
5. Ignition switch - OK in my experience but suggested by someone else as a
likely cause.
6. Voltage regulator - unlikely in my opinion.
7. Other wiring/connectors/components.

You must try (1) and (2) first. I recall there was a nack to coaxing the
switch & rheostat from the dash but can't remember the details. Are there a
couple of pinch-barbs round the back of each? Anyone?

(1) - (4) are things that I've done in the past to help recover my lighting.
They are all reasonably simple and will cost little more than your own time.

(1), (2) & (3) were undertaken together, therefore not really possible to
say which was the culprit part. They collectively cured my dash flicker.
(3) cured my headlight flicker.
(5) - (7); just attempting to summarise other people's (no doubt excellent)
suggestions.