The easiest way is to get a chromatic tuner. Something with a built in mic. (so you don't have to plug in to use it)
Basic easy tuning goes like this
A E A, G D G, E B E, Basically the top and bottom strings are in the same key. (the difference in string gauge makes them sound different, but still the same)
Without a tuner I make the top string sound good to my ear. Then match the middle and bottom string to the same key. then I go back and tune the middle string up until it sounds right when all three are strummed. ( As it climbs in pitch it will all the sudden sound really good. ) The increased tension from the middle string will usually pull on the neck, and require a lil adjustment of the bottom string again to bring everything back together.
#2. Playing with a Slide
The biggest mistake a see new players make is the pressure used when playing with the slide. You Do Not Need To Push The Strings All The Way Down! You only need to push hard enough to make the strings sound clear.
Another tip I have found to be helpful with slide guitar. Is to slide into the note your playing. Don't try to hit it on the head. Just slide in from a lil below. It gives you a lil room for clarity. And provides a nice bluesy tone too.
I will try to add videos over time.To help out. Thank you for checkin out LittleJohnsCBG's!!!!