Africa

In July, the Northern Hemisphere is in the middle of summer: in North Africa there's the monsoon at tropical latitudes and in the Sahel, while the Sahara is fiery-hot; in the Red Sea it's also very hot. In Cape Verde the rains may start in the second half of the month. In the Southern Hemisphere it's winter, and even at tropical latitudes it can be a little cool. The cities you can visit, are almost all found in mountainous tropical areas of the Southern Hemisphere, or around the Equator.
Where to go: Brazzaville, Dar es Salaam, Harare, Kampala, Kigali, Libreville, Lilongwe, Luanda, Lusaka, Maputo, Mbabane, Nairobi

Asia

In July, it's mid-summer, and it's hot in the vast areas having a continental climate, while the monsoon ruins the weather in much of South-central and Eastern Asia, but spares some parts of Indonesia.
Where to go: Jakarta, Kuala Lumpur, Lhasa, Omsk, Singapore, Ulaanbaatar

North and Central America

It's mid-summer in North America, and it's the warmest month, therefore the best one, in northern lands. It's often too hot in the United States, and sometimes even in Southern Canada, except on the Pacific Coast, which is cooler. In California and Baja California it's sunny, but sometimes the hot Santa Ana wind blows, especially on the southern coast, while in inland areas the heat is intense. In the Gulf of Mexico and in Central America the weather is hot, muggy and rainy, and there's some chance of hurricanes.
Where to go: Anchorage, Ilulissat, San Francisco, Seattle, Vancouver

South America

In the Southern Hemisphere in July it's midwinter. In the north of the continent, in the Northern Hemisphere, it's summer, so it's hot and rainy. In the Andean zone, from Ecuador to the south, it's the dry season. You can go to cities that have a tropical or sub-tropical climate, where the winter is mild or pleasantly warm.
Where to go: Asunción, La Paz, Quito, Rio de Janeiro, Sao Paulo

Europe

July is the central month of summer, and is typically the warmest, albeit slightly, compared with August, especially in Northern and Central Europe. The days are still very long in Nordic countries; sometimes it can get hot in Central Europe, while in Southern Europe the sunshine is guaranteed, but to visit cities it's often too hot. However, there is no shortage of rain in Northern and Western Europe, where Atlantic disturbances can still pass, while in Central Europe, afternoon thunderstorms are fairly frequent.
Where to go: Amsterdam, Berlin, Brussels, Copenhagen, Dublin, Edinburgh, Helsinki, Geneva, Kiev, London, Ljubljana (first half), Luxembourg, Minsk, Moscow, Oslo, Paris, Prague, Reykjavik, Riga, St. Petersburg, Stockholm, Tallinn, Tórshavn, Warsaw, Vilnius

Oceania

It's winter in the Southern Hemisphere, which means that it's the driest and least hot season in tropical islands. In Northern Australia it's the dry season, so it's the best period, even though it is hot. In Brisbane and the Gold Coast the weather is mild.
Where to go: Brisbane, Darwin, Papeete, Port Moresby