It's amazing what you find when you dig through your old collections! I happened to come across this old IF timetable from 1985 and I thought I'd run through a few of the salient points:
The vast majority of IF's routes operated to and between Soviet "satellite states". The fleet consisted of IL-62s, Tu-134s and IL-18s, with Berlin's Schonefeld Airport as the main base.
There were routes to "western countries": Amsterdam, Scandinavia, Austria and Turkey, plus some routes to "political allies", in Africa.
"Regional" routes were offered from Leipzig, Dresden and Erfurt, with an IL-18 service operating from the latter to Moscow-SVO.
SXF-SVO was the most important (possibly the busiest) of the airline's routes and it was one of very few routes operated by Aeroflot's IL-86s. Interflug flew a mixture of Tu-134s and IL-62s on the route. IF operated an average of the five flights a day.
Interflug's IL-18s operated a number of routes: apart from ERF-SVO, above, other routes included: SXF-Kiev, Minsk, Tatry (Czechoslovakia), Bratislava, BUD (also from LEJ and DRS), Bucharest, Varna (also from Erfurt) and Bourgas.
IL-62 were operated on flights to ATH and on longer haul routes, such as Havana (nonstop), Addis Ababa (then a "political ally", under Col. Mengistu) - via Cairo and Khartoum, Hanoi (via Karachi), Algiers, Baghdad and Luanda (via Lagos).
Foreign travel was, of course, tightly controlled, and one had to be "politically reliable" to be allowed to leave. The Stasi, as is now known, kept tight tabs and had a very active informer network.
Interestingly, the airline also offered a "salon service", which was basically a business charter service, using Let-410s.
The configurations of the fleet were as follows: IL62 (8F, 150Y, with the 8 F seats in the middle, just forward of the wing), Tu134 (76Y) and IL18 (100Y).