The go-to resource that is usually suggested is The Mind Illuminated by John Yates. I found it to be a very nice tutorial-like guide to meditation with hardly any spiritual/religious bullshit, and it breaks it down into stages so you get some idea of where you are at and what progress you are making (even though progress is not really something you should be focusing on with this).

The introductory course on the Headspace app I also found good but I think it is better to not stay on it beyond that.

If your thoughts keep you awake sometimes I think you would definitely benefit greatly from this.

The Waking Up app by Sam Harris is a great way to get started - there is an introductory course I found very helpful.