Do you concentrate best in the morning or are you hopeless until after lunch? Are you always too tired to think properly after 10pm or do you love that quiet time with no distractions? Work out which times are best for 'thinking' activities (reading and writing) and which are best for 'admin' activities (searching and organising).
Are you a sprinter or a marathon runner? Do you work best with a deadline looming or does that stress you out? Acknowledge your working patterns and plan your time accordingly.
Use a grid or a diary (paper or online) to work out when you are busy and when you could work. Even half hour slots may be useable. Be realistic - give yourself some time off!
Find out all your deadlines and put them in your diary.
Using all of the information you have from the four points above, and working backwards from your deadlines, fill in the available times in your diary with 'SMART' targets (see below) for each session.
SMART stands for Specific, Measurable, Attainable, Realistic and Timely. So instead of planning to 'do research' or 'write some of the essay' during a 1 hour slot you should be more specific i.e. 'read and make notes on two articles' or 'write a paragraph on point B (200-300 words)'. That way you know what you need to do and you will know that you have achieved it. This is better for keeping motivated too.
It is easy to waste slots of 10 or 20 minutes because we don't think we have enough time to get anything done (waiting for things to start or people to arrive, sitting on a bus etc.). These time fragments can actually be useful if you plan ahead. For example, you can use the time to find a suitable article on your phone; read a paper; brainstorm initial ideas for an essay etc. Keep a notebook with you or use an app on your phone and you can fill these wasted moments and save time when you could be working on something more complicated later.
When you are too tired to work on something complicated, use the time to organise your workspace, your notes, your files etc. It will save time in the future (as you will be able to find what you need) and make you feel more able to work on the 'thinking' tasks when you are more rested as you won't be tempted to tidy up instead.