You can find the iliac crests by placing the sides of your forefinger/hand in the fleshy part of the waist at the level of the umbilicus, move inferiorly and the first hard lumps you feel on each side are the iliac crests. L4 spinous process is at the level of iliac crests - 1 on bottom picture.
Greater trochanter of the femur
Move inferior from the iliac crests down the most lateral part of the hip. The first hard lump you feel is the greater trochanter of the femur. You can check by rotating the leg.
Anterior superior iliac spine - ASIS
In supine from the anterior midline of the thighs move superior. The first lump you feel will be the ASIS on each side.
Move inferior from the umbilicus it will be soft and then you will eventually feel the bones of the pubic arch. Often easier to get the client to find it for you.
The sacral spines can usually be felt easily on the midline
The outline of the coccyx can be felt in the cleft of the buttocks.
Posterior superior iliac spine - PSIS
In prone, easily found by moving superior and medially with the thumbs from the mid part of the fleshy part of the buttocks. Try to feel up and under the PSIS on each side. You are at the level of S2. Another extremely useful landmark.