Please click on the link below and read the entire site carefully. Then follow the instructions to the letter.
In a nutshell:
• Calibrate and profile your monitor. Set the resulting profile as your monitor profile. Never use a device independent color space (such as ProPhoto RGB, Adobe RGB or sRGB) as your monitor profile. Only use your calibrated profile specific to your monitor.
• honor the embedded profile in each file;
• when sending your images to a run-of-the mill lab, convert your images to sRGB (do not use assign profile; use CONVERT to profile) and embed the sRGB profile in them.
The above site explains it all to you.
Wo Tai Lao Le