The mainstream attire of urban Lithuanians increasingly replicates that of the Western Europe and it is acquired in the same franchises (opened ~2000s).
The richest go to Milan and Paris to shop, while the small town "elite" visit main cities and famous local designers. The less well off shop at marketplaces and used clothing stores (where a good suit may be bought for less than 1 Euro if you know when to visit).
Main clothing subcultures in Lithuania
Parallel to the Western trends there is a more glitzy female fashion (more colors, shorter skirts, higher heels, more make-up), somewhat more popular in smaller towns and among the ethnic minorities. It dates to the 1990s when people were hungry for colors, glitz and less conservativeness (denied to them for decades by the Soviet regime). Even many male businessmen preferred red suits in the 1990s (unlike the female fashion, this has since died out).
People considering themselves to be more fashionable (i.e. imitating the West more closely) tend to denounce such "over-the-top" clothing as "Gariūnai fashion" (after the Gariūnai market in Vilnius suburbs where most Lithuanians started their businesses - and used to acquire clothing - back in 1990s). A female that dress that way is known as fyfa, usually a pejorative. The male "style-counterpart" of a fyfa is forsas or marozas. They emphasize their masculinity by extensive use of sportswear, even for a simple walk or a night out (prestigious nightclubs ban this). Muscles and cars are also parts of their image.
Fyfa and forsas may be considered a subculture with an Eastern European flavor. Other parts of Lithuanian youth have embraced Western subcultures since the 1990s, each with its own clothing aesthetics, preferred musical styles and festivals. They include goths, hippies, punks, "metallists", "street culture" (hip hop), skinheads, ultras and LGBT.
Fashion under the Soviet occupation
Modern glitz likely would have not became so popular if not the decades of clothing limitations under the Soviet occupation (1945-1990). Make-up for female school students and long hair for males used to be banned, for example.
Furthermore, there used to be a constant shortage of goods, including good clothes. There have been merely a few designs readily available (all conservative) - therefore most people of the same age dressed similarly. To avoid this most women used to knit and sew extensively well until 1990s. Additionally the few people privileged enough to be allowed abroad (especially to the non-communist states) used to shop there for their relatives (or buy goods for illegal resale).
Older women may still dress in Soviet style-clothes or knit/sew but these practices are much less common after the advent of independent Lithuania and free market.
Formal vs. informal clothing in Lithuania
Under the Soviet occupation formal attire was required on many occasions, e.g. in theaters and restaurants, for students during all exams. Today Western practices have largely been adopted and there are less suits in streets.
Folk costume is acceptable as formal attire under the Lithuanian etiquette. Such usage grew in popularity in 1930s (women in full folk costume, men with folk strip replacing their tie) but has been since extinguished by the Soviet occupation. Today the folk costume usage is limited to folk singing and similar events. Prior to the 20th century the folk costumes were used by most Lithuanian peasants; they are characterized by white shirt under a colorful jacket (exact patterns depending on region). Women wear long patterned skirts (shorter for folk dances), men use trousers. Women also cover their hair with scarfs.
Uniforms are uncommon: few schools have them and many jobs that tend to be uniformed elsewhere (e.g. bus driver) allow workers to dress freely.
Lithuanian clothing and fashion industry
Lithuania used to be a powerhouse of clothing manufacturing. However the lack of radical overhaul of models after independence created an image problem ("outdated local clothing" vs. "modern foreign clothing"), while Asia could not be outcompeted in costs, leading to the industry's decline in 2000s.
On the other hand a Lithuanian haute-couture scene developed and some designers reached some fame beyond Lithuanian borders. "Mados infekcija" is the regular fashion festival for young talents.