I know it can be overwhelming to think about being in charge of your child's whole school day. You might want to try to copy what they were already doing in public or private school, if they were previously enrolled. Perhaps you will think back to how things were when you were in school (if you can remember!). Maybe you would like a simple formula like "reading, writing, and 'rithmetic".
Download/print this worksheet to help you plan!
I'll help you figure this out. First up, find out if there are any subjects required by your state homeschool laws. In my home state of Texas, we are required to teach math, reading, spelling and grammar, and a course in good citizenship. So first I will be sure those subjects are covered. We will work on HOW to teach those subject a little later. For now, let's just sketch out a plan of what will be included in your school day.
Next, or especially if your state does not have subject requirements, be sure you are hitting all the basics. I think we can all see the need for reading, math, spelling/grammar instruction. But what are we missing? Well, even though they aren't required in Texas, any college will expect your child to have been taught science and history so you will want to add those kinds of subjects in now.
If your children are in elementary school, you have some room to play with what you include. If you have an upper level student, especially a high school student, you may want to think about high school credits and graduation requirements for your state. There are no homeschool graduation requirements in Texas, but I can easily peek at the state graduation requirements for public school students and get some ideas of what to include.
Next, there may be some other subjects you would like to add in. These might not be full-time subjects, but something you plan to hit on a few times a week or for just a semester. Typing is an example that comes to mind. It's not exactly a fun elective-type class, nor is it usually considered a core subject. However, most parents would agree that it's a subject they want to cover with their child.
Lastly, let's consider the fun stuff! These would be called electives in the upper grades or "specials" in the lower grades. These are subjects like P.E., homemaking, photography, etc. Just be careful not to over-schedule these. You will find that homeschooling takes much less time than school in a traditional classroom, so your child will have extra time to pursue their own interests. These can easily count for electives. One of our daughters loves making stop-motion movies and has a YouTube channel where she does just that. Just allowing her the free time needed to pursue this hobby has built up enough hours to count as a high school elective. Also, we cover a lot of this fun stuff in the "But what about..." section of the website. You may find some ideas there.
In making your subject plan, you might want to jot some notes at the bottom for skills and behaviors you want to work on this school year. For example, perhaps your young child can't tie her own shoes yet. Make a note so that you remember to set aside time to work on that skill.
Here is a good site for figuring out what needs to be taught at each grade. It's just one opinion on what should be included, but I have always found it helpful when I start planning. Remember to download/print the Subject Planning Worksheet to help you.