Here are 5 quick ways to improve your sight singing skills.
1) Practice identifing notes on the Staff and on the keyboard. Drill yourself until you can recognize them in your sleep.
2) Learn how to identify key signatures in sheet music using the order of flats (b) which is B, E, A, D, Greatest, Common Factor. The second to last flat in the sequence is the key signature. For key signatures with sharps (#) the sequence goes Fat Cats Go Down Allys Eating Birds with the key signature being a half step up from the last sharp.
3) Download pictures of the solfeg hand signs and practice singing Do Re Mi Fa Sol La Ti Do while making the signs with your hands. Remember that you can start on any note as "Do" (also called the tonic and name of the key signature as well) and sing the scale in any key you want. Then simply write in the solfeg for any song that you've identified the key signature of.
4) Practice your rythms. When practicing, remember that each type of note (whole, half, quarter, 16ths..ect) is composed of shorter notes of half its value and that dotted notes add half of the note's value. Also, remember to practice and recognize triplets and any other tricky rythms that you might have trouble recognizing right away.
5) Once you are comfortable with all those individual parts and pieces, put them together and practice. As with any learned skill, practice is essential.
Good luck everyone and happy practicing!!:)