There's a thread already with a lot of in-depth information that could be useful to you if you want to understand the way samurai works.

But if you want the tl;dr version, practice using your Gekko, Kasha and Yukikaze combos to build up Sen (the three samurai icons) to use powerful attacks. 1 sen lets you use a DoT, 2 is an AoE, 3 is single target burst. Use Hissatsu:Kaiten to boost your damage in these finishers. Keep your buffs up and running. Use Meikyo Shisui to quickly build up Sen and Hagakure to convert these sen into Kenki (your sword gauge), so you can use Shinten and Guren between attacks. Remember positionals so you don't waste kenki generation. Use Third Eye everytime you know you will get hit so you can get an additional attack with Hissatsu:Seigan, or health back with Merciful Eyes.