I like to create designs that are relatively close to historical accuracy, at least in appearance of the overall design of the garment. Here are a few paintings and costumes that I will base my own off of.
Portrait of Queen Ann Boleyn. Notice her signature "B" necklace.
Catharine Howard, Ann Boleyn's cousin and Henry VIII's 5th wife. I like the trim around her neckline.
Katharine Parr, yet another wife of Henry the VIII. This shows me how long to make the sleeves and a good view of the dress front.
Princess Elizabeth from the film Crossed Swords. I just love this gown! I can't say anything about the accuracy but it's pretty.
Beautiful Tudor gown I came across while researching online.