Start with how you read
Voice acting is acting. Producers are not buying a nice voice; they are buying a convincing read of a script. Before equipment, learn to read copy so that it sounds like talking, to hit a line the same way twice, and to take direction.
Read aloud every day. Record yourself and listen back the way a producer would, for the first ten seconds. Notice where you sound read instead of said.
Train with someone who works in the field
A coach or a course gives you something you cannot give yourself: someone who hears the habits you no longer hear. Look for a teacher who works in the kind of voice work you want, and who will tell you plainly where you are. The guide to choosing a coach goes through what to ask.
Pick one or two kinds of work
Commercials, narration, audiobooks, animation, games, e-learning and telephony are cast by different people listening for different things. Beginners often do better by starting with one or two and doing them well, then widening. If you are unsure, record a little of each and see which one sounds most like you.
Build a quiet place to record
You do not need an expensive studio to start. You need a quiet room, a decent microphone and interface, and a space that does not echo. A wardrobe with clothes can be a start; many people then build a small booth.
Listen for noise you have stopped hearing: fridges, traffic, computer fans. A clean recording matters more than expensive gear.
Record a first demo, and make it the right size
A demo is a short set of clips that show how you sound on the work you want. Make one demo per kind of work rather than a mixed reel. The demo reel guide covers what goes in, what to leave out and how to order the clips.
Put your work where people can hear it
A voice actor needs somewhere to send people: a page where the reel plays at once, with a short line about who you are, your studio and a way to book you. That is what a website is for. The voice actor website guide goes through what it needs.
Find your first jobs
Work comes from casting platforms, agents and direct clients, and each takes patience. Start by auditioning regularly, writing to producers who suit your voice, and keeping a list of who you have contacted. The guide to voice acting jobs has more on where to look.
What to expect
Progress is slow at first and then faster. Keep recording, keep listening back, keep your demo current, and keep track of what you are booked for, so that your next reel leans into it.