It seems that everyone is scared of UART0, and are therefore jumping though hoops to use UART1, which is significantly less performant.
Here's how you set up UART0...
1 - set up GPIO14 & 15 to use alternate mapping 0 (this may already be done at boot, but it doesn't hurt to redo it)
2 - Stop the uart by writing 0x0 to the CR
3 - Clear any outstanding interrupts by writing 0x7ff to the ICR
4 - Calculate the baud rate divider and fraction as follows:
divider = UART_CLK / (16 * baud)
temp = (((UART_CLK % (16 * baud)) * 8) / baud)
fraction = (temp >> 1) + (temp & 1)
UART_CLK is fixed at 3000000 for the Pi hardware
5 - write divider and fraction to IBRD and FBRD repsectively
6 - configure fifo enable, bits, parity and stop bits in LCRH
7 - reenable the UART by setting the RXE, TXE and UARTEN bits in CR
8 - enable the UART interrupts as necessary
Example code to do this is available on the ARM site (AN256 covers using the TX interrupt, DDI 013 covers the rest).