When you have all these necessary travel papers in order (your passport and visa to Japan) you can start looking into getting tickets. You will want to determine which time of the year you intend to visit Tokyo, to determine the sort of clothes you need to carry with you, and what sort of weather waits for you upon your arrival. The seasons in Japan are pretty distinct and this is good to know because you want to be able to pack for the right season you will be going there.
To make the most out of your Japan trip, the best time to enjoy the mild climate would be during springtime from March to May. This happens when the famous cherry blossoms of Japan are on full display and the days are temperate enough to tour the main districts and side thoroughfares. These months are comfortably warmer without being uncomfortably hot. You will want to make sure to pack a sweater for the evenings when it can get a little chilly.
The end of April and the beginning of May has notably more tourists of the international and local kind, with the Golden Week of Japan in full swing. The Golden Week, as it is called, is the period towards the last week of April to the first week of May, when concentrations of national holidays are observed. It may well be the busiest time of the year in relation to the city metropolis receiving visitors. This is probably best avoided especially if you want to experience a more personal, more personalized visit to the city.
To allow for an unimpeded journey in discovery of the city metropolis and the surrounding prefectures of Tokyo, pack a small umbrella for each person on the trip. A light, rainproof jacket is also advisable for any unexpected showers you may get caught under.
The summer months are experienced between June to August and this can be a pretty challenging weather if you are not used to the heat. Even those used to experiencing this sort of heat try to stay out of the oppressive humidity when they can, locals either go off to places where the weather is cooler or look for places where they can enjoy beach fronts. It is still pretty usual for Tokyo to experience chance showers, so be ready and prepared for any sudden weather changes. Make sure that you pack clothes that are comfortable, and light. Make sure that you do not carry anything too heavy that will not dry up easily in case of a downpour.
September is not the best time to move around in Tokyo since this is usually the time of year when the weather can be more unpredictable and the city is more prone to typhoons. It would probably be wisest to hold off your traipse around the richly historical, and electrically charged city metropolis. You will have a better bet of enjoying the off-beat vibe of Tokyo around October when humidity is lower compared to the summer months but still find it comfortably snug as long as you bundle up well. Winter in Tokyo is crisp, and clear. The city metropolis hardly, if it ever does, get snow so if you were looking for an alternative venue for a White Christmas you will probably have better chances going further up north to the island of Hokkaido, considered as the Alps of Japan.