I usually just...say it. ._. Like, "over the next few months, blah blah went on until whatever day" or "a year later, character people were in yada yada".
Why...would you not? Is that a thing people do, just timeskip without mentioning it at all??
I guess I see how it could work, but I feel like timeskipping is a stylistic technique in and of itself, and it's kind of weird for me to think about people doing it without wanting to draw attention to it.
Like in a movie, when you do the panoramic shot over the crimson fall leaves to show that the year has progressed since the last scene, or in an anime, when you show the characters looking older with new outfits...it elicits a feeling in the audience, a sort of sentimental "aw, everyone's growing up, things have happened" reaction. And you can't really get that in prose unless you step out of the narrative a bit and explain it outright.