How to make a cake less dense
What you are making is a pound cake. Or maybe a sponge cake, depends on the order of mixing the ingredients. Of the two, the sponge cake is somewhat lighter, so if you have been making pound cake (cream butter and sugar, add eggs, then flour), you can switch to sponge (foam eggs and sugar, add flour and fat). But both are hearty homemade cakes, they are supposed to be dense. 

The iced cakes you get in a bakery are much lighter, because they use a different type of layer. Most types of cake are lighter than pound and sponge cakes. Try making genoise, chiffon, or angel food cake layers, they are all light. And yes, using cake flour will help too, or replacing part of the flour in the recipe with pure starch (usually cornstarch or potato starch, you can also use wheat starch if you can get it. Tapioca or arrowroot aren't that well suited). For a real "pro" taste, also throw in some lecithine, it makes the mouthfeel softer and smoother - but if you don't feel like hunting around for lecithine, don't bother, a good homemade cake doesn't really need it, I only mentioned it because you asked about "cake made by a pro".