If you want to make your flight more realistic, there are several ways that we may overlook or forget, but are crucial for the experience, plus finding tips through IF’s tutorial page is tiring lol.
follow flight level guidance
most of us already know this, but depending on which direction you are flying you have to fly at specific Flight levels. anything flying east or moving easting in anyway must fly at an uneven flight level, such as FL310, FL330, FL350 etc.
for anything moving west must stay at an even flight level such as FL300, FL320, FL340 etc. south and northward directions sometimes do have their own restrictions but aren’t necessary
(these restrictions dont really apply FL150 or lower)
follow airspace restrictions
following airspace restrictions may add flight time, but does bump up realism points. airspace restrictions can very is size, shape, severity or country registration. Afghanistan is a good example of airspace restrictions. some countries declare the entire country a no-fly-zone entirely. countries such as Germany restrict flights only under FL330, or the US who marks the country as a no-fly-zone except for the north-east panhandle. it is good to check websites for airspace restrictions
if you would like some more tips, I might make a follow-up topic for this