[header] How to write a sympathy thank you [title] Buy cards with envelopes. [step] The colors and design should generally be subdued. Since you are writing a personalized note, choose a blank card or one with very little text; an abundance of trite ready-made phrases will depersonalize your gesture of thanks. 
[substeps] Alternatively, you can send a plain note. This is especially appropriate if you feel you have a lot to say.