The 1900 through 1930 censuses lists the individual's year of immigration to the United States. Don't be surprised if they are all different dates.
Visit the cemetery and take a picture of the tombstone. However, be aware that not all cemeteries allow taking photographs. Another reason to know the rules for a specific cemetery that you intend to research.
Use a good genealogical software package to maintain your records and your digital files.
Use a Correspondence Log for both regular and electronic correspondence. This includes the name and address of the person to whom you have written, what you requested, the date the request was sent, and a column for the outcome. Remembering every letter written is impossible. Follow up if you don't get an answer within a month.
[Sources & Evidence]
Cemetery Form: These sheets are useful for people who wish to keep track of information in graveyards or sexton’s records.
[Charts & Forms]