Ah, Gantt charts! I <3 Gantt charts. They are so very useful.
They enable you to list the tasks that you need to do. You then order then according to what needs to be done first etc. Then you allocate time to each task. The allocation of time can overlap. Some tasks may be independent of each other and so may run concurrently.
I used this to plan my wedding (some years ago)!
SO, write out all the tasks you need to do for your major project - then break down tasks into individual things that need doing. Group your tasks according to linkages, then order any tasks that can be ordered. Then estimate the amount of time you think you will need to do each task and block it in.