The Uzbek part of the Ferghana Valley is in the center of the valley, and in the extreme southeast of Uzbekistan. The whole valley, both this part and the parts in other countries, is on the main route of the old Silk Road route between Kashgar and Samarkand.
There is only one way to the Ferghana Valley and it is heavily guarded. You can get to Ferghana with taxi from Tashkent. You can find taxies going there near bazaars. The price is around 30,000 sums. Crossing the border of Ferghana there is a checkpoint where they check passports. Foreigners usually are registered, but there should be no problem.
Note: when going through tunnels there and in area around you cannot photograph or use a mobile phone. The police will stop you and you might have some problems.
Taxies from certain points of cities go to all other cities. There also microbuses.
Ferghana is a strongly Islamic region, so dressing should be modest.