To me it makes no sense to send tanks without first sending planes, drones, and anti-tank weapons. They could use some A-10 Warthogs to knock out the Russian tanks, but they need F-16's for fighter cover to protect them. Also, drones, especially battlefield drones to see where the enemy is and help knock out their tanks, trucks and supply vehicles. Tanks to be would be the last thing to send after getting good air support. Then use the tanks with infantry to take back their territory, especially territory with the majority Ukranian population. Only a couple of provinces in the east and Crimea were majority Russian speaking. Crimea has deepwater ports and air bases. The two eastern provinces are where most of Ukraines mineral ores are located. Thus you see why Russia wants them as well as Crimea. If Russia only took those to start with, and left Ukraine alone, there might not be a war going on, but a lot of diplomatic talk. Russia wanted more, as in all of eastern Ukraine, as well as all of southern Ukraine. This turn Ukraines resolve against Russia and also most of the rest of the world.
Russia had already taken Crimea in 2015 with very little backlash from the west. They could have probably taken the two eastern provinces the same way. But no, they had to try to take more. Even Russian speaking people in liberated areas have turned against Russia.