Forward folds are one of the staple groups of yoga asanas. Whether standing or seated, forward folds can create length in the spine, combat the compression of gravity, and promote inward reflection and introspection.
Alignment is key for forward folds. A slight anterior tilt of the pelvis to keep the low back from overly rounding should be encouraged. Engaging the abdominals will protect the lumbar spine and engaging the quadriceps will protect the hamstrings. Many students will require a small bend in the knees during forward folding as well.
It's important to prepare the spine and hips for forward folding. Teaching pelvic tilting to students to help them identify where their pelvic and spinal neutral are is imperative. A great set of postures to teach pelvic tilting is cat/cow as it allows students to feel a full anterior pelvic tilt, a full posterior pelvic tilt, and pelvic neutral. In a forward fold you want a continuous and even curve of the spine. A great way to teach this is in child's pose.
With regards to sequencing, standing forward bends are more appropriate to warm the spine and stretch the hamstrings prior to moving into seated forward folds. In standing the pelvis isn't fixed to the floor, which allows more freedom of motion to move into the forward fold position and evenly distributes the lengthening across the spine and hamstrings. Seated forward folds, such as paschimottanasana or upavishta konasna, are best performed after the forward fold has been explored in other postures.
Forward folds may aggravate previously existing conditions such as bulging or herniated discs and hamstring strains or tears.