The sutra says that you should meditate, i.e. consider and think about, four concepts:
- the body
- the mind
- objects of the mind
The sutra is quite structured and it helps writing the structure down. It is also quite dense however and makes a lot of cross references to other Buddhist concepts. You can use this sutra therefore as a crossrefence and skeleton to other Buddhist ideas. Below is a simplified outline. Hope this helps.
1) The body
Consider mindfulness of breathing (in/out, slow/calm/...)
Consider the postures of the body, i.e. know that you are sitting when you are sitting and standing when you tell someone else off :) (while standing that is)
Consider mindfulness with clear comprehension, i.e. know that you are stretching when you are stretching, bowing when you are bowing, ....
Consider the repulsiveness of the body, i.e. blood streaming through your veins, through your body, urine, puss, etc....
Consider that your body is made out of four elements (earth, water, fire, air). This needs translation into the modern world.
Consider the nine cemetery reflections. These are descriptions of how the body decomposes from a dead body through to dust. It is a meditation on death that can be quite powerful.
There are pleasant, unpleasant and neither pleasant nor unpleasant feelings. Worldly as well as spiritually.
3) Contemplation of consciousness
Consciousness refers to 51 mental formations. "Feelings" is one of them already discussed above, so it can be discounted in this category. The 51 mental formations are categorized as universal, particular, wholesome, unwholesome (basic and secondary), and indeterminate.
For each formation, acknowledge it, look deeply into it, see the impermanence of it, see how it leads your thoughts to inter-being.
4) Contemplation of mental objects
4.1) Consider the five hindrances: sense desire, anger, sloth and torpor, agitation and remorse, doubt
4.2) Consider the five aggregates of clinging: material form, feeling, perceptions, formations, consciousness
4.3) Consider the six internal and external sense bases: eye/form, ear/sound, nose/smell, tongue/flavour, body/tactile feeling, mind/mental objects
4.4) Consider the seven factors of enlightenment: mindfulness, investigation of mental objects, energy, joy, tranquility, concentration, equanimity
4.5) The four noble truths: suffering, the origin of suffering, the cessation of suffering, the road to the cessation of suffering
The sutra concludes with a discussion on the sort of time that is required on your behalf to understand it. And in classical manner, it puts it between seven years and now :)