A good way to get started is to buy a distressed home as your primary residence. Once you fix it up you can either turn it into a rental or sell it and buy another primary and hopefully have enough left over to buy a rental. Benefits for buying as primary; you get a better interest rate, you can put less money down, and by living in it, you get to figure out how to fix sh!t on your own time. You can live without a bathroom for a week or two but a tenant can't. (yes i've done this, the grocery store down the street got to know me real well)...
As for timing, if a 2010 ever comes around again, buy as much as you can. Until then, buy a property that will cash flow from day one or has a lot of value add to it. I remember trying to buy off of the MLS back in 2006/07 i kept getting blown out of the water on my bids and was like who the hell is paying this much for those properties?? I ended up finding two off of Craigslist, i flipped one and still have the other and its doing great as a rental. So you can make money on the top of the bubble if you buy what makes sense.
Unless you have a lot of money sitting around, it takes years to build a strong rental portfolio. Start now and let time be on your side, nothing like paying you 2018 mortgage with market rents from 2038. if you bought right in 2018, you will be killing it in 2038.