Carbon nanotubes exhibit exceptional physical properties at the individual scale. In order to optimize these properties at the macroscopic scale, a good control of both the dispersion and alignment of the nanotubes is required. In this work we study the dispersion and alignment of single-wall carbon nanotubes in lyotropic nematic suspensions and we use these suspensions for the elaboration of anisotropic thin films. Individual nanotubes are stabilized by denaturated DNA in aqueous suspensions. Lyotropic nematic phases are prepared by concentrating nanotubes/DNA aqueous suspensions and the nematic is shear-aligned in thin cells. At each step of the preparation, the dispersion and alignment are studied by polarized optical microscopy, photoluminescence and Raman measurements. We show that thin homogeneous anisotropic films can be prepared from wet aligned suspensions. In a first series of experiments, the nematic and the corresponding films exhibited a quite weak order parameter (S about 0.2) [1], which was assigned to some entanglements of the nanotube network. In this talk, we will show that the order parameter of the nematic and the corresponding films can be significantly improved by controling the aspect ratio and/or the bundling of the nanotubes, for example using fractionation through controled ultra-centrifugation during the nematic phase formation. [1] C. Zamora-Ledezma, C. Blanc, M. Maugey, C. Zakri, P. Poulin, E. Anglaret. Nanoletters 8 (12), 4103-4107, (2008).