What are the EASA external aircraft lighting requirements for day/night/VFR/IFR operations?
For EASA (via europa.eu, Easy access version), which is very similar to ICAO Rules of the Air (Annex 2):

SERA.3215   Lights to be displayed by aircraft
(a) Except as provided by (e), at night all aircraft in flight shall
display:

anti-collision lights intended to attract attention to the
aircraft; and

navigation lights intended to indicate the relative path of the
aircraft to an observer and other lights shall not be displayed if
they are likely to be mistaken for these lights; or

in the case of balloons, position lights.


(b) Except as provided by (e), at night:

all aircraft moving on the movement area of an aerodrome shall
display navigation lights intended to indicate the relative path of
the aircraft to an observer and other lights shall not be displayed if
they are likely to be mistaken for these lights;

unless stationary and otherwise adequately illuminated, all
aircraft on the movement area of an aerodrome shall display lights
intended to indicate the extremities of their structure, as far as
practicable;

all aircraft taxiing or being towed on the movement area of an
aerodrome shall display lights intended to attract attention to the
aircraft; and

all aircraft on the movement area of an aerodrome whose engines
are running shall display lights which indicate that fact.


(c) Except as provided by (e), all aircraft in flight and fitted with
anti-collision lights to meet the requirement of (a)(1) shall display
such lights also during day.
(d) Except as provided by (e), all aircraft:

taxiing or being towed on the movement area of an aerodrome and
fitted with anti-collision lights, to meet the requirement of (b)(3);
or

on the movement area of an aerodrome and fitted with lights to
meet the requirement of (b)(4);   shall display such lights also
during day.


(e) A pilot shall be permitted to switch off or reduce the intensity
of any flashing lights fitted to meet the requirements of (a), (b),
(c) and (d) if they do or are likely to:

adversely affect the satisfactory performance of duties; or

subject an outside observer to harmful dazzle.



You might want to refer to a country's specific AIP just to be sure that there aren't local differences.
Not to be used in lieu of the above, AIP, or airport textual data, what follows is my summary by light type:

navigation lights:

in-flight at night
moving on movement area at night
stationary and inadequate area illumination


anti-collision:

in-flight by day and night
taxiing; being towed -- unless too dazzling; generally in busy controlled airports the ATC will ask for them to be switched off; see (e)


red beacon (or similar):

engine running day or night on movement area