First, let me say that these two issues should be covered in your initial hospital orientation. I cannot believe they were not better covered when you were in school.
Observe IV insertion site at least once/hour.
Look for signs of infection - reddness, swelling and drainage.
Look for signs of phlebitis - edema, red streak along vessel, warm to touch, pain.
Look for signs of infiltration - swelling, leakage at site, no blood return, pain.
If any of the above signs are present - D/C IV catheter, elevate extremity, apply warm soaks. Follow your hospital's policy on infiiltrated IV's. Reinsert IV in a different site, preferably in the opposite extremity.
As for body mechanics -
Find your center of gravity and maintain it.
Do not bend over from the waist; bend from the knees (squat).
Hold a heavy object close to you - not at arm's length.
Never lift a patient by yourself, no matter how small the pt.
Never be afraid to ask for help.
Hope this helps. Good luck with your career!