Find your rhythm, the essence of acoustic blues, which evolved from the African sense of timing and dance. When you are playing acoustic blues, there is no drummer. In the juke joints of the prewar era, the guitar player was the "band" and was responsible for rhythm.
Learn to play percussively. Some players tap the guitar for a drum effect. Others snap the bass strings by pulling them with a thumb. Both are done for rhythmic enhancement and emotional effect.
Develop an appreciation for the history of acoustic blues. Blues evolved in three regions of the southern United States. Each of these developed its own style of blues, as illustrated in Mississippi by Charlie Patton, Son House and Robert Johnson; in Texas by Blind Lemon Jefferson and Leadbelly and Lightnin' Hopkins; and in Piedmont by Blind Willie McTell, Blind Boy Fuller and Rev. Gary Davis.
Focus on one or all three acoustic blues traditions. Within each tradition is great diversity. Once you are familiar with each tradition, certain players will influence you more than others.
Choose the right instrument for the style of acoustic blues you wish to play. For example, the 12-string guitar was often used by the Piedmont players but less so by the Mississippi bluesmen, who instead tended to use the bottleneck guitar.
Learn to use a fingerstyle technique rather than a flat pick. Some acoustic blues players use thumb picks. There is no rule for how many fingers you should use. In the Piedmont style, the relationship between the thumb and fingers is more complicated than in the Mississippi or Texas style. In Mississippi blues, the thumb often plays the role of the drummer, using the bass strings percussively.
Develop your fingerstyle technique. In Piedmont style, the thumb continually plays a walking bass line while the fingers pluck a melody. The best way to develop this technique is to play chords in the first position, such as G, C and D, and use your thumb to pluck the bass strings in a consistent pattern.
Learn how to play in different tunings. The three primary tunings used to play acoustic blues are standard tuning (E-A-D-G-B-E), open G (D-G-D-G-B-D) and open E (E-B-E-G#-B-E). Open tunings are an integral part of acoustic blues.
Consider adjusting the tunings if you are playing a 12-string guitar. You can use the same tunings; however, most 12-string players tune down one or two whole steps to relieve the tension on the guitar. This produces an interesting effect through the combination of having 12 strings and playing in a lower register.
Practice your slide technique. One of the reasons that open tunings are so popular in acoustic blues is that they make playing bottleneck or slide guitar easier. Place the slide on the third or fourth finger of your left hand. Without pressing down, place the slide over the fret of the note you wish to play.
Play individual notes on each string, and then practice sliding from note to note. Lay the other fingers of the left hand down on the strings behind the slide. This prevents unwanted overtones and noise.
Play in open tunings without the slide, concentrating on various rhythms. Then play with the slide to complement your rhythmic patterns.