Disguise seems to be a dominant recurring motif in nearly all of Shakespeare's themes as characters for very different purposes dress up and assume another role in order to trick or deceive other characters. Let us examine just a few examples.
Firstly, if we look at Viola in Twelfth Night, we can see that she dons a male disguise for protection initially. She has entered a new environment as a defenceless female, and there is clear indications that there is a sense of unrest. Adopting a male disguise therefore is something she does to protect herself until she can work out what to do next.
In The Taming of the Shrew, disguise is something that is definitely important in the Induction, when poor Christopher Sly is made to believe he is a lord by the various disguises that are adopted by the real "lord" and his servants. This is of course done to amuse the lord at Sly's expense.
In Romeo and Juliet, Romeo and his friends disguise themselves to enter the masquerade ball at the Capulet mansion. They do so with the intentino of having a good time, but of course the disguise is something that becomes very important as it allows the two lovers to meet and fall in love.
These are just three examples of the different ways in which disguises are used in Shakespeare's plays, but you could easily examine any play and look at disguise as a theme and consider how it impacts the action. I have included links to the three plays I have discussed below to help you analyse them further.