This is to support the answer by idrougge: "geographic names in new settlements are usually quite uninventive." I live in Australia, which was settled mostly by people from Britain. Of course, in Australia there were already Aboriginal people, and quite a few place names derive from local Aboriginal languages (often as mis-heard by British settlers). I don't know if your scenario includes pre-existing language-using inhabitants: if so there is another source of names, which can look completely different from the Slavic-derived names.
If I just look at non-Aboriginal names, a lot of them are names of people, often politicians in power in Britain at the time (Melbourne after Viscount Melbourne, Sydney after Viscount Sydney), or prominent early leaders in Australia (Governor Macquarie gave his name to several things, including the Macquarie River). The suburb of Collingwood in Melbourne was named after either Baron Collingwood (a famous British admiral) or after the Collingwood Hotel (which was named after Baron Collingwood and was an early building in the area).
The rivers aren't generally named after British rivers. The Darling River was named after the then Governor of New South Wales, who instigated an exploratory expedition. The Murray River was named after a British politician. The Murray and the Darling are the two biggest rivers in Australia. The Diamantina River was named after the wife of the first Governor of Queensland. The Swan River in Western Australia was the first place that black swans were seen by Europeans.
Another big category (probably the biggest) is names of somewhere in Britain, such as Ascot, Richmond, Perth, Newcastle, the Grampian Mountains, Pentridge (which was the name of a notorious jail in Melbourne, but is an English place name). Very few of these have "New" in their names; they just took the British name unaltered. The State of New South Wales is an exception. New Norcia was established by Spanish Benedictines, and named after Norcia in Italy where St Benedict was born. The town of Clunes acquired its name from a local farming property called "Clunes"; the name is originally Scottish. The suburb of Coburg was named to commemorate the visit of the then Duke of Edinburgh, who was a member of the royal house of Saxe-Coburg and Gotha. Bacchus Marsh was named after an early settler, an Englishman called Captain Bacchus. Vaucluse was named after the first homestead in the area, Vaucluse House, which was in turn named after a poem by the 14th century Italian poet Petrarch. The suburb of Wyoming was named after a once popular ballad, written when Wyoming in the U.S.A. was a Territory (not yet a State). Note that not all the names are ultimately British (though most are); the British absorbed influences from other cultures, as did the Slavs.
Names that arose locally: Bald Hills, Poverty Point, the Snowy Mountains, Mount Disappointment, Mount Misery and Mount Hopeless (in three different Australian States), Diggers Rest and Miners Rest, Airport West (it is a suburb). There is a locality called Dead Horse Gap in the Snowy Mountains, but I don't think anyone lives there. Kangaroo Valley and Emu Plains are named after native fauna. Chatswood was named after Charlotte Harnett, wife of a pioneer in the area, and was originally called "Chattie's Wood", "Chattie" being Charlotte's nickname, and the area being forested then (now it is a very dense urban area).
The gold rush in Australia gave rise to various names such as Golden Square and Canadian Lead. The town of Research (originally Swiper's Gully, then Research Gully) was so named because after the gold rush started the area was re-searched (searched again), and gold was found. Poverty Point was renamed Golden Point when gold was found there. I think the Radio Springs Hotel was named after radioactive springs in the area, which were considered to be therapeutic.
Some names are just inexplicable, such as the Sydney suburb of Dee Why.
Why have your Slavic people settled this planet, and have they been there a long time? What is the history of the settlement? Who sent them originally? Were they convicts or prisoners, were they fleeing oppression, or were they just trying to make better lives for themselves? Was the beginning of the settlement really difficult? Are there strange flora or fauna? Did the first settlers carve out large estates, naming them however they felt like, which afterwards gave their names to towns? Was there something like a gold rush or other significant event?
Maybe Australian names will give you useful parallels.