Sundays in the park means that much of the park is closed to street traffic,
Therefore, if you are driving, street parking will fill up quickly. Mind the street signs.
Also on Kirkham and Lawton around 8th, 9th, 10, 11th there is usually parking and it is a quick down hill walk to the park. There is also parking (especially early) at Ocean Beach at Fulton and Great Highway. Then take the bus east from Great Highway --> Lincoln. Link to SF MUNI here.