Think about what you like. Also, think about what you like, but lacks something to make it special, and what you might do to make it special for you. Have a plan, and structure a blend with the kind of tobaccos you like in percentages you think you'll like. Always make very small batches, then let them marry for a couple of weeks.
Write down everything you do. if you make something that's close, you can tinker with the percentage of whatever tobaccos you need to to get closer to what you really want. Trial and error is a great teacher.
Most of all, smoke every varietal you get straight so you'll understand their properties before blending.