When to visit
Milan, depending on how you want to tour the city, is virtually visitable all the year. Keep in mind most places, including tourist destinations and museums, are closed on Mondays.
In autumn, the weather is warm/cool, and in later months can be quite rainy and foggy. At this time of the year, the city's inhabitants are very busy with work, so, the only people you're likely to see wandering around are tourists. All the major venues and shops are opened, since it is the working part of the year.
In winter, the city can become cold often below or around zero degrees centigrade, and the weather is usually foggy and rainy if not snowy. However, the city, in the few weeks before Christmas, becomes delightful to visit - the main sights are all illuminated by stunning lights, a huge Christmas tree is set up in front of the Duomo, vendors and markets can be found everywhere, many shop and display windows are decorated and the streets become bustling with locals and tourists alike. However, the only downside is that it can become extremely crowded, noisy and busy.
In spring, the weather is similar to that of autumn. People go back to work, and the atmosphere becomes more quiet, yet serious unlike that of the winter. Parks become nice to visit, as trees blossom. The city is also quite nice to visit at Carnival, where people dress up and celebrate, and during Easter, where there are special services held in churches and some special events.
In summer, Milan can become extremely hot and humid, with the odd powerful rainstorm here and there. Whilst in July, apart from the weather, most shops remain open, in August, as many locals go off to take their summer holidays, many businesses and venues shut down with the notice Chiuso per ferie, or shut down for vacation. The city may become quite empty with the odd tourist strolling around, and with several of the main sights shut down. Despite it's not the best time for shopping and the weather's not at all times very pleasant, it's good if you want to enjoy the city to yourself when it's quiet, and maybe want to stroll around, sipping at the odd open bar or at an ice cream, or walking in a silent park. Despite many businesses shut down, some still do remain open, and you will still be able to find some open shops, restaurants and museums.
Understand
If Rome represents the "old" Italy, Milan represents the "new" Italy. Milan is the most modern of all Italian cities, and it still keeps most of its past history intact.
At first sight, Milan looks like a bustling and relatively stylish with its shiny display windows and elegant shops metropolis, with a good number of grand palaces and fine churches in the centre, but might seem like a slightly prosaic, soulless and business-orientated place. It can be quite rainy, grey and foggy, and some of the buildings, ancient or modern, have quite a severe appearance. Whilst there are a lot of parks, Milan looks as if it has very little greenery, and apart from the very well-kept historic part, many areas are indeed quite scruffy and dirty. However, Milan, unlike most usually historical European cities which throw the sights in your face, requires quite a lot of exploring - take it as it is, and you might enjoy its fashionable glitter and business-like modernity, but might find it not very "captivating". If you spend time, though, strolling through less well known areas such as the pretty Navigli, the chic Brera district, the lively University quarter, or some of the smaller churches and buildings, you'll find a forward thinking, diverse city filled in every corner with history, and with a plethora of hidden gems. Plus, with such an established history in theatre, music, literature, sport, art and fashion, there's really not much you can miss.
Milan, as many have noticed, doesn't fully feel like a part of Italy. Despite the similarities between typical Italian cities such as Verona or Venice with the city, it does have a different atmosphere. Milan feels more like a bustling, busy, fashionable business capital - where in several cafes, lots of people only stop to have a quick espresso at the bar counter, and where tourists at times seem even more laid back than the locals. Milan, unlike the traditionally red-terracotta roofed Italian cities, is quite grey, as many buildings are constructed using limestone or dark stones. Ancient buildings mainly have a sort of Austrian/Germanic neoclassical look with some slight French influences. However, with some cycling around in old fashioned bicycles, restaurant chairs and tables outside at summer filled with locals and tourists alike, and people strolling down the pedestrian avenues, licking an ice cream or carrying some heavy shopping bags, Milan does boast some "Italian flair".
These differences between Rome and Milan are evident from several proverbs, such as an Italian saying about the differences of the two cities which roughly translates, "Rome is a voluptuous woman whose gifts are very apparent, while Milan is the shy, demure girl whose treasures are plentiful, but discovered in time."