When to go visiting Egipt?

Well, it depends on many different aspects. The best time to go to Egypt is between October and April, and especially in December and January. The months to avoid, in principle, are June, July and August because of the heat weather. Do not take all this as a rule, it is just a general advice to avoid extreme high temperatures and the sands storms, that may represent a dramatic change in the outlooks of your visit.
So, plane it carefully with time in advance just to make the best of your holiday. Furthermore, you have to take into account that Egypt is a Muslim country, and therefore, one of their main devout times, the month of Ramadam, is widely observed especially in these times. Consider that the Ramadam is a movable pious time that changes every year, so before planning your visit takes first a look to the calendar just for knowing when does Ramadan falls at the time of your vacation.
Of course, Egypt is a country that receives tourists by the millions every year, and Egyptian people is more than happy in general to receive and help tourists during their vacation, but the more you will plan your trip, the better it will be.