How do i split an incoming string?

Contrarily to other answers, I'd rather stay away from String for the following reasons:

• dynamic memory usage (that may quickly lead to heap fragmentation and memory exhaustion)
• quite slow due to construction/destruction/assignment operators

In an embedded environment like Arduino (even for a Mega that has more SRAM), I'd rather use standard C functions:

• strchr(): search for a character in a C string (i.e. char *)
• strtok(): splits a C string into substrings, based on a separator character
• atoi(): converts a C string to an int

That would lead to the following code sample:

// Calculate based on max input size expected for one command
#define INPUT_SIZE 30
...

// Get next command from Serial (add 1 for final 0)
char input[INPUT_SIZE + 1];
byte size = Serial.readBytes(input, INPUT_SIZE);
// Add the final 0 to end the C string
input[size] = 0;

// Read each command pair 
char* command = strtok(input, "&");
while (command != 0)
{
    // Split the command in 2 values
    char* separator = strchr(command, ':'))
    if (separator != 0)
    {
        // Actually split the string in 2: replace ':' with 0
        *separator = 0;
        int servoId = atoi(command);
        ++separator;
        int position = atoi(separator);

        // Do something with servoId and position
    }
    // Find the next command in input string
    command = strtok(0, "&");
}

The advantage here is that no dynamic memory allocation takes place; you can even declare input as a local variable inside a function that would read the commands and execute them; once the function is returned the size occupied by input (in the stack) is recovered.