It will take alot of practice. Knowing the right amperage settings on your welder helps greatly. MIG is easiest to learn, stick and TIG will take more practice. If you can stick weld than the others will be very easy for you with a little practice.
You should get scrap metal and practice horizontal, vertical and even upside down welds. Make sure you have the best type of welding mask and make sure the lens are clean (they get dirty from welding spatters, dust, grease, ect). Make sure you can clearly see what you are welding. Once you know how to work the bubble (molten metal) you will get smoother welds. It does not hurt to get some pointers from welders themselves or at some welding course but in the end getting proficient at welding comes down to practice, learning to work your welder settings combined with hand-eye cordination.