This is obviously conjecture since I am not a senior official in the Russian government and cannot speak on its behalf. Russia likely plans to disintegrate Ukraine (non-militarily). It's not out of the realm of possibility to have a plan as follows:
- Position troops on border
- Border states cooperate and ask for annexation in exchange for peaceful resolution
- Move troops into new regions
- Repeat from step 2 as Ukraine government becomes smaller each step and eventually caves
From an international point of view, there isn't really anything you can do if a state decides that it wants to become a part of another state (of course you can decline such an offer if it's your state they want to join). So the strategy is to coerce them into "voluntarily" joining the Russian state. A bloodless conquest.
Why this strategy works? You can pin the idea of interference into a sovereign state's internal affairs if you try to get between two nation's private agreements. Since Russia has not fired a shot, any retaliation would make them look like the defending party, justifying use of force. And of course, the third party isn't actually important enough for other parties to use military intervention. The third point is actually the idea here, Salami Tactics. No one is going to escalate to a nuclear war, so an offending party can make repeated small offenses just up until the threshold of retaliation.
Now the US probably recognized that this is going to happen, so they have preemptively started sanctions even without Russia firing any shots into Ukraine. But there seems to be some misinterpretation with the current situation in regards to NATO. For one, even Ukraine recognizes that the self-determination clause is a joke. Ukraine cannot join NATO simply because it wants to. Ukraine can only join NATO if it wants to any all of the other members of NATO want it to. Which obviously, is not the case (otherwise it would likely already be in). Second, notoriously trigger happy countries (e.g. USA) have clearly stated that they do not intend to send troops to Ukraine which means that in the case of an actual invasion, they will wait until the conflict reaches NATO borders, which Russia is well aware of and is why they are adamant on Ukraine staying out of the military alliance. The "retaliation" is ineffective at best. The reality of the situation is that countries like the USSR, Iran, and DPRK have almost always been under economic sanctions and learned to live with them as an economic reality. So announcing the worse that you're going to do is not a deterrent if Russia is prepared to live with those sanctions. Russia is also, of course, not new to western sanctions. Just like the other aforementioned countries, any gaps in economics can be filled by a not US aligned country like China or India. As can be obviously seen in the last couple of years, the US is even afraid to economically retaliate against China so sanctions against China for trading with Russia is not going to happen.
All in all, this is a pretty safe play, with the optics of being "peaceful" as the strategy doesn't require actually using your force, just projecting it by moving it around territories you control.