Pick a hardware type
Each type locks you into a different range of coins, costs, and noise levels. Start here.
Purpose-built silicon for one algorithm. Best income per dollar on big chains, but locked to that chain forever.
Off-the-shelf graphics cards. Lower per-watt income than ASICs, but you can switch algorithms or resell to gamers.
Your existing computer's CPU. Realistic income is cents per day. Mostly worth it on Monero-family chains.