With May wrapping up next week, now is the time to be starting up your holiday SEO strategy.
It seems far away right now, but since SEO can take awhile to get going you should always be looking out 5-6 months at a time. It's now about 6 months until Black Friday.
Start working on your pillar content, talking with other websites about backlinks, research which keywords you're going to target, and get everything else ready.
For a bit of an easy boost, make sure you have JSON-LD for SEO installed as soon as possible. It can take Google awhile to award Rich Results but they can be a real traffic and conversions boost. Especially during competitive times like the holidays.