My favorite way is by Sigil. You should really know how to banish and cleanse first so you don’t get a parasite instead though, by getting your spiritual hygiene first, then developing your astral senses and avoiding impostors and parasites… When you can be sure you’ll not get attacked by parasites, then try Unofficial Tutorials: First Contact from Sigils to Evocation Collection.
I encourage you to actually read those links, ten pick the methods that call to you to try.
Offerings - absolutely nothing. These are not actually desired by the entities, they just make humans feel good about themselves. I never give offerings any more, but I do like incense and that can be considered an offering.
Time - any tome you can get off your butt to do it. The best time is always now.