I imagine Russia will avoid direct ground conflict wherever possible (you risk losing life in a 'fair fight') and simply use complete air superiority to bomb from the skies and move in when a target area is rubble and possible resistance is minimised. As per Russia and US tactics in Syria; US and British in Iraq etc. This way you can maintain public support by keeping your casualties at well below 1% of the foes while dismantling their military and giving them a good old dose of 'collateral damage' and 'shock and awe' from the skies

. It means progress will be slower, but Putin has all the time in the world as nobody will come to Ukraine's aid.
Ukraine must devote resources on the separatist border but, if things go badly, pull back to the heartland (Kyiv) before they risk having those forces cut off. Then be realistic about next steps and focus on a protracted guerrilla war in urban areas. They must also keep a channel open to Poland to allow refugees and potentially a de Gaulle like government-in-exile. Russia will soon show if the priority is Eastern Ukraine or the entire country and Ukraine must take serious decisions in response about their own priorities. Better 15 million people ripped out of a law abiding democratic life than 41 million.
I doubt Putin is doing this simply to extend gains in Eastern Ukraine (Kharkiv) but I wouldn't completely rule that out yet. To have the entire world denounce you and do this you must be thinking big in terms of full regime change and territorial merger with eastern Moldova and (current worst case scenario over the longer term) Kaliningrad, the latter of which would entail NATO territory. But he can take his time and evaluate his options with little rush.
The democratic world must effectively remove Russia from the global trade system, pressurise China to limit their assistance and give Ukraine as much support as possible in terms of supplies, military advice, housing of refugees and medical assistance. It must also bolster the hell out of the NATO border and discuss matters urgently with non NATO nations like Finland and Sweden, to offer them the option of membership.
I thought I would see these sorts of lawless days in the 2030s, not in the 2020s. I hope Ukraine can give Putin a bloody nose to force a reconsideration of present and future military goals. But with no airforce and seemingly limited air defences it is hard to see how this can be achieved.
The UK media complaining that wheat prices might rise and the cost of pasta might go up tells you everything about the level of ignorance, discourse and general empathy for our fellow man here. Overall I think we have leaders at present in most other major democratic nations to create a reasonably coherent response, but if you are in Eastern Europe and not within NATO territory you should be very nervous.
We must accept US intelligence has been proven accurate and that they were not crying wolf. If so, that means full invasion, death lists of pro-democracy figures and a puppet regime with someone like this fellow.
en.wikipedia.org
Incredibly bleak times.