By bus
There are three types of shared public transportation in La Paz: regular buses or "micros"; shared vans, called "mini buses", and shared taxis running set routes advertised on the windshield, called "trufis". The former cost Bs 1,30 while the second are Bs 1,50-2,30 depending on duration. A trufi will generally cost you Bs 3 to 3,50. All types have their routes indicated on the windshield, but mini buses have the bonus of fare collectors hanging out the side, yelling out routes in a rapid, auctioneer-like manner. You can hail a bus or mini bus anywhere; to get off, just yell out "¡voy a bajar!"
By taxi
The easiest way to get around is by taxi. They aren't metered, so agree on a fare before boarding; a ride within downtown should be about Bs 6-8. If you want to go further, ask two or more taxi drivers before boarding. A normal ride by taxi from downtown to a place within the city won't cost more than 20 Bs.
By foot
If you ever find yourself to be lost, in general the easiest thing is to simply walk downhill. You will eventually find yourself on the Prado or another main avenue, then You'll be able to take a taxi to the downtown, if you are on the southside of the city (Zona sur)