What do you really need to know?
You just need to create a series of "historical" events, starting from where, in you history, the USSR stayed together.
It could be as early as Trotsky gaining power of the party, and not Stalin.
Then you need to look at and decide what happened during WWII.
Or maybe after Stalin Beria managed to keep power, killing the others, with Krustjev getting the axe first.
Perhaps Gorbachov never come to power, and instead some other hardliner.
Of course after '91 things get stickier:
Desert Storm never occured.
Jugoslavia is still in one piece, and Germany isn't unified. The EU isn't really going anywhere, again, and the Euro isn't.
Enormous forces are located around inside Europe, and you can't travel through Germany without seeing an airbase, armoured vehicles, or NATO.
The economic downturn in Europe during the early 90s is so pronounced; Germany doesn't have to pay for reunification.
The peace process in the middle east isn't. Pakistan and India still have the bomb. and still shoot at each other.
Al-qaida is not the reknown terror organisation it became, as Usama didn't get quite so upset at USA, because they never sent US troops to Saudi Arabia.
On the other hand, it is probably likely a puppet regime still sits in Afghanistan, beleaguered by mujhadeen fighters, sponsored by CIA and Iran..
South Africa probably still has a apartheid regime, and the fighting in the Congo, and Ethiopia, Eritrea, and Sudan never occured, or at least at a much lower intensity.