Avila is a popular day trip from Madrid, but it is also an excellent stop on the way to Salamanca.
If traveling from Segovia to Salamanca, I recommend a stop here for a few hours to see the city walls. See Avila Pictures.
Avila to Salamanca by train
The train from Avila to Salamanca takes around an hour. There are trains throughout the day. No need to book online but you can do so from renfe.Avila to Salamanca by bus
The bus takes one-and-a-half hours and costs around 8 euros. You can book from Avanzabus.Avila to Salamanca by car
The drive from Avila to Salamanca takes about an hour, via the A-50.Read aboutRenting a Car in Spain or Compare Prices on Car Hire in Spain.
I recommend going from Avila to Salamanca in my Around Madrid Road Trip.