Your heading tag H1 should include the most important keyword that you wish to rank for. Let H1 tag be to the exact readable length and must not be too long. Your H2 and H3 tags must also include relevant or similar keywords related to your H1 tag. All your H1,H2,H3 tags must be logically sequential and paralell. Modify the structure according to your requirements. Do not add too much of keywords or too much of header tags as that is highly not recommended.