Of the many techniques I read about, the following seemed the most convincing to me:
1. Improve your physical and mental conditions.
2. Remove distractions from reading device and environment.
3. Locate important bits of the text. Hotspots help (sub-heads, bold, italics, graphs)
4. Push self to read fast
1. Read phrases instead of words, which needs avoiding sub-vocalisation
2. Use a guiding tool (finger, pen or index card)
3. If the text is familiar (topic, characters, style), ensure you do a flash mental review before you read.
If said reading is important and worth remembering, make a short note. Perhaps a tl;dr version.