Tag with washing and fabric information is often found on the back of the wide end.
6 general tips
If you cant get it clean or are afraid of ruining it, you should deliver it to a professional dry-cleaner.
When you get a stain on your tie you need to act fast. The longer you wait - the worse it will get to remove it.
Remove, cover or throw your tie over your shoulder (if appropriate) when you are in situations where you know it can get dirty (eg. holding a baby, eating "messy" food).
Treat your tie with a specialized fabric protection spray before wearing it.
Some times it can be easier and cheaper to just throw the tie away and buy a new one.
Always read the washing instructions (if any) before trying to remove a stain.