Since you prefer not to confess your attraction, use flirting as a fun first step to assess whether the interest between you and your crush is mutual. Take flirting slow and watch how your crush responds. Flirting will telegraph your initial interest while avoiding some of the awkwardness of rejection if it’s not mutual. (Know, however, that if the flirting progresses and you seek to take it to the next level, eventually you will need to acknowledge having some feelings for your crush.)
Here are a couple of tips. Amp up your physical appearance and what you wear. This will improve your confidence around your crush and get their attention. The color red attracts special notice when worn by either men or women. Smile and make steady eye contact. Offer your crush sincere compliments. As you talk with your crush, try to subtly move a little closer, more into their personal space -- if you sense that they are comfortable. Use appropriate levels of touch if you sense that it is welcome. For example, when sitting next to them, graze their arm or leg with yours in a non-obvious manner. Pretend to pick a hair or lint off their shoulder or touch their hand lightly.
Reading your crush’s signals are very important. When you flirt, pay attention to whether your crush seems disinterested, confused, or pulls away or if instead, they return your flirtations with flirty gestures of their own. The more they flirt back, the more you can turn up your charm.
If you want to know more, my article http://hubpages.com/dating/Get-Noticed-The-Scie...... describes the importance of five critical factors in getting noticed as a potential dating partner: 1) what you wear, 2) smiling, 3) eye contact, 4) strategic use of interpersonal space, and 5) touch.