1) Find the legal requirements for your state. You can get info on that from HSLDA, as elliemaejune said, and depending on what state you're in, the requirements may range from just a letter of notification, to record-keeping and yearly testing.
2) Find or put together a curriculum. There are many homeschool curriculum providers, and probably the best way to find out which curriculum to go with is to take a look at a few and see which you like best. Homeschool conventions or local homeschool groups can help with that:
3) Do the work, and if necessary, keep a brief record. You don't have to follow the school year schedule - many homeschoolers work year-round and do less hours per day (3 is probably average for core subjects). One big advantage of this is you have more time for extracurriculars and/or a job. Or you could do a month on and two weeks off, or whatever schedule you like best.
If there are any subjects you can't handle on your own, online or community college courses are an option. I highly recommend community college for things like lab science and Calculus, and online courses will do fine for some other things.
4) Take nationally standardized tests - AP, CLEP, or DSST - for as many subjects as you can. While a portfolio of work is usually accepted at colleges, the simplest way to prove you know your stuff is just to take a test. You're more likely to get college credit with test scores in hand.