So purely from an equipment perspective, look for a lens that has a lower f-stop (lets in more light) at the zoom levels you need. These get expensive pretty quickly...
Exactly
Try RAW format images, get a higher capacity card.
Check you have a full frame sensor in that camera. Better / larger area sensor = better pics
Not so cheap but for T2.8 its really not bad.
Sigma 120-300mm f/2.8 EX DG OS APO HSM AF Lens 136101 B&H Photo