San Miguelito is in Rio San Juan Region of Nicaragua.
San Miguelito (sometimes called "San Miguel" by the locals) is the other municipio in the Rio San Juan departamento with a coastline of lake Nicaragua. It sees few tourists, but can be a good intermediate point on a trip from the capital to San Carlos
There is a direct bus from San Carlos that goes to the town itself
All buses connecting Juigalpa and San Carlos as well as those that go on to Managua can drop you of at the empalme from there it is roughly two kilometers to downtown, so make sure to get a cab or have somebody pick you up
The boat that connects Granada, Altagracia (on Ometepe) and San Carlos stops here after leaving Ometepe the ride is both longer and more expensive than by bus and depending on the direction of travel you might arrive in the middle of the night.
There is no airport in town, you can fly (domestically) to San Carlos and Ometepe and take the bus or boat from there as described above.
The carretera from San Carlos to Juigalpa is in a reasonably good state and you should be able to find the empalme. Be careful as both pedestrians and people on horses use the street and it can be hard to see them especially after sunset.
There's an annual bull and horse festival some time in March