This is where mindfulness in our daily life can be very helpful. We can have a usual thing we do, if nothing special is happening; we can go through our dedication, our five reflections, Compassion/Lovingkindness, but what we decide to expand on will often be decided by our awareness of our mind during our daily life. At least that's what I've found, that's what I've encouraged people to do. Sometimes when people are not sure about what to do, I will often say, "Well, try to do a Sympathetic Joy once a week; Compassion/Lovingkindness needs to be done more often; don't forget to expand the reflections from time to time so that we can get a deeper understanding of these things". However, our awareness of our normal waking mind and what's coming up for us in our daily life will often encourage us to go into formal reflections about certain topics.
For example, if you find you are getting lost in a lot of doubt, you may have to do more confidence inspiring objects. If you are not really seeing that you have the capacity and this is too difficult, then it may be helpful to remember to do the Ten Paramis reflection, Sympathetic Joy, the Buddha, Dhamma, Sangha until you see some of these doubts lessening in your life. If you are getting worried and carried away with the future with worry and fear, it may be helpful to go into a longer form of the reflection on death and impermanence to balance this tendency to worry about the future. If you see that you're having fear of fame arising, then it maybe helpful to do an in-depth reflection on the eight worldly dhammas, concerned with fame and obscurity and combined with death.
So the awareness in our normal life of what hindrances are arising for us is very helpful for deciding what we need to expand more fully in our formal practice, to be able to note them and be aware of what is motivating us each day. It would be helpful to decide before we start the formal practice, but if in the middle of it you are doing the normal five reflections and then you realize: "I seem to be drawn to this death reflection tonight", and you start to see the mind being more attracted to the short form of death, often that's an indication that it's helping to balance something there. So you can make a note of that and then start to expand that. That is what I have often found. Sometimes I'm expanding all of the five short reflections and the mind really seems to grab onto one. At that particular time, it is sometimes an indication to me of what I really need at that time. Or if for some people it's not grabbing onto one, then that may be an indication that that's what they need, depending if they are getting lost in attachments.
Some people find this is a bit too "free form" and like more form. If you have a tendency to be like that, then it is helpful to actually give yourself more form. Some people do need this. If so, then it may be helpful to make a whole list of the reflections so we don't forget them. Consult them sometimes and ask, "Now, have I done this lately?" Another meditator was quite innovative and made a list and cut them all out and put them in an envelope, so they could just pull one out and think, "That's a good one to do". So you can get very innovative as many old students have, to see what works for you