Study and imitate country music singers. Imitation is not the goal, it is a step along the way. The goal is to develop your own style that makes you instantly recognizable. Singers, and musicians in general, develop their skill and craft at first by listening to and imitating their heroes. Stealing vocal licks and ideas - phrasing, tone and dynamics - from a variety of influences give you a palette for creating your own sound and style. There is a wide spectrum of vocal styles in country music, Hank Williams, Buck Owens and Merle Haggard, Patsy Cline and Tammy Wynette just to name a few.
Find the right range and tone for your voice. All singers have a particular range that suits their voice. Singing within your range allows you to sing naturally without straining and the sound of your voice will also be fuller. All songs are sung in a particular key or tonal center such as C major, E major, A-flat major or D minor, F# minor and B minor. Sing a few country song in different keys. Ask the piano player to play the song in the different keys and find the keys that best suit your voice.
Take lessons with a professional vocal coach. A professional vocal coach help you to develop and improve your voice. You will learn basic things such as proper breathing technique and correct posture, you will learn how to singer more powerfully and how to control and use your voice, and you will develop a deeper appreciation and understanding for music overall. If hiring a vocal coach is impractical or too expensive, consider online singing lessons.
Record and listen to your singing voice. Listening to a recording of your voice is remarkably different from listening to yourself as you are singing. A recording gives you a critical and objective insight into the quality of your voice. Listening to the recording helps you to identify pitch problems and phrasing problems. It is also a good way to experiment and find the right tone and feel for a particular song. Sing and record several versions of the same song. Study and listen to the recording and see what works the best.
Sing as much as possible in live performances. Singing live in front of an audience is an essential step in developing confidence and experience. Form a country band and book as many gigs as possible. Sing at open mic nights. Learn to play the guitar if you don't know how already.