If you get a 1099 then your employer considers you a contractor, not an employee. Whether or not that's legitimate is
another question, but for our purposes here it means you'll be your own little business unless you want to fight with your employer over the classification.
You'll need to remember that you'll pay self employment tax. 15.3%.
For mileage, just keep a log of miles driven and the purpose. You can deduct
54.5 cents/mile from your income. If you want, you can also keep track of actual expenses and deduct that based on the proportion of business vs personal travel instead of the standard mileage rate, but unless you have a fancy car and/or poor gas mileage I suspect you'll be better off with the standard rate.
I'm not too familiar with meal deductions, so do some more research, but the key point seems to be whether you're considered to be away from your tax home, which seems to mostly hinge on whether you have a period of rest (like staying overnight at a hotel, but can be shorter) before returning home. It looks like
Publication 463 has lots of good information including examples. There are also meals for entertainment if you're paying for a meal for a business associate. It seems like in either case (away from home, or entertainment) you can only deduct 50%, of your meals, but this can be either actual cost or based on federal per diem rates, so it seems like there could be opportunity for some arbitrage there if you have overnight travel (research that though as it almost seems too good to be true). As far as I can tell, it seems pretty clear that if you're only gone a normal workday, and the meal isn't an entertainment expense, then it's not deductible. Also remember that this is only a deduction, so the government is only footing the bill for your marginal tax bracket times the 50% of the per diem, so you're still spending money that you might not have to if you didn't eat out.
If you have a space in your home that you can set up for exclusive use by the business then you can also take a home office deduction. If you own your home then you might consider using the simplified method ($5/sq ft up to 300 sq ft) as it avoids issues with having to pay back depreciation recapture if/when you sell. If you rent then using actual costs in proportion to the business use will probably work out better. If you own you may still want to use the standard method, just know that the depreciation will come back to haunt you when you sell.
The other advantage to a home office is for mileage. You can't deduct commuting mileage, which can include things you wouldn't normally think of as commuting, so if you have a home office and you make sure you do something business related in it as the first and last thing you do during the work day, then the travel between the home office and your home is the commute, and any driving is therefore business mileage.
Here's a good explanation.
You can probably also get a deduction for your health insurance. My wife supplies our health insurance through her employment, so I don't know much about this, but I'm pretty sure you can deduct the cost of marketplace plans from your business income if you're self employed.
You might also consider opening a business retirement account. If you don't have, and don't expect to have employees other than owners and their spouses in ANY business in which you are an owner in the future, then a solo 401k is the clear winner as it lets you put away the most as compared to the amount of income. If you think there's a good chance you will be an owner in a business with non owner/spouse employees, then you'd probably be better off with a SEP IRA. If all of your current savings is already in tax advantaged space and you'll need more than your self employed income to live off of, then you can ignore this, but if you need less than your self employed income or you have a taxable account, then getting as much as you can into tax advantaged seems like a good idea.
If you'll make enough you might want to consider setting up an S-corp (or LLC taxed as an S-corp) since that can help you avoid some self employment tax, but I'll leave that discussion to someone else more familiar like
@SeattleCPA. The reason it doesn't work at lower income is both because the S-corp costs money that needs to be made up, and you have to earn enough that you can still pay yourself a "reasonable" salary in while still taking some of your income as distributions.
That's all I can think of right now, but taking a look through
Schedule C might give you some other ideas. And remember, I have experience with some of this, but I'm shooting from the hip with some of the deductions I don't take, so do your own research.
