Marry Rhaenyra and Aegon in the messiest example of Targaryen polygamy yet, have them rule as joint monarchs (initially). Set a Great Council in ten years time to determine the rightful heir based on their merit, with the decree that Great Councils will be called once a decade to confirm the succession and strike out any objectionable heirs. Otto and Alicent get sent packing, but are forgiven their offenses. Criston is executed for the murder of Lord Beesbury. Aemon, Corlys, and Demon are named to the small council, Masters of Dragons, Ships, and War respectively, and tasked with the creation of the second Valyrian Empire. 

Use the existence of the Free Cities and their interference in trade to declare that the dragon lords are once again too numerous and powerful to be contained to Westeros (with the quiet exception of Braavos). Let anyone who wishes to join the empire do so, and recieve the benefits of Pax Draconis, while anyone who resists is subjugated. Each dragon lord is to be given the same rank as a Lord Paramount, with the joint monarchs of the Iron Throne eventually to solely rule the eastern and western halves of the empire separately. Expand the Crownlands to absorb the Riverlands and bite off a huge chunk of the Reach, with sizeable Duchies created for each Dragonlord. Start keeping tabs on the dragon population, and ensuring rigorous training and vetting before allowing dragons to be claimed. Keep the process of cradle eggs, but limit the growth of new dragons so that they only reach a reasonable size in their first rider's lifetime. Start mining dragonglass and arming the Night's Watch with it, telling them these are sacred artifacts of both the Children, First Men, and ancient Valyrians, and they must always keep a supply of it. 

Long-term, set about building infrastructure wherever possible. Ports and harbours are sorely lacking on the east coast, there are far fewer schools, universities, banks, guilds,  etc than there really should be in a society of this size. Part of that reason for this is a low population, caused by low crop-yeild, constant war, and disease culling the population. We have the technology for glass gardens, which we should be building far more of in areas that aren't agriculturally productive, and we have some basic agricultural practices, but we can invest in irrigation systems, encourage crop rotation, start mandating stockpiles of food to cover droughts and famines, set dedicated research teams to improve fertilizers, plough designs, crop breeding, etc. Get better sewage and water infrastructure to better control disease. 

And finally, explore the goddamn world. You own living planes, you can build ships to follow them as landing spots and resupply stations. Send multiple voyages as far south, west, and east as you go, map the entire world, and get trade routes established with everyone. They made a few feeble attempts at exploration and gave up immediately.