Plans are imprecise. Plans are flawed. Plans are necessary.
"If you want to amuse god, tell Him your plans," goes the old saying. But in business, plans are the pillar stones of finances. They dictated everyone's future.
You start with basics: How much can you grow? How much should you grow? Remember, you can't work more than 24 hours a day. But maybe you can charge more. Or sell more intangible stuff. Revenue is a product of price × units.
Plan for your sales. If each unit needs worker's time, count it. If each shipment needs a pair of shoes and a cardboard box, that's what you account for. Every incremental cost that increases with sales should be planned for.
Add fixed costs. You pay your IT guy. Rent an office, pay for a server. Remember that even-though those costs are fixed, they will eventually increase. Either because you'll need another office, or the rent will just increase.
When planning your expenses, think about what you are getting. Maybe your marketing budget is little too tight to support your dream revenue. Or maybe you can't reasonably manage so many workers alone. Make your assumptions make sense.
And then just add it all together. Your master plan will now dictate marketing budget, hiring and personnel budget and all other steps you are planning to make in the year. Subtract any financing cost and taxes and you will have your targeted net income.
A word to the wise? Start with revenue. You can sell (for) more.