Birds can be extremely shy and you may quite easily disturb them, sometimes without realizing that you a doing this! Their sight and hearing are often far better than ours. So in open field, forest, near rivers or wherever the birds may be, always use appropiate camouflage and move slowly and quietly. A rare shy bird may be close by. From time to time halt, listen and look around, also behind you.
Be careful in special situations like near ditches, bush, walls, big trees, water, etcetera. Some shy birds like Woodcock (houtsnip) or Green Sandpiper (Witgat) may not fly until you almost step on them.
Always make use of as much natural coverage as you can get. When you halt, try to be in front of or near trees, bush or any other object. Make your silhouette part of surrounding nature.
Make sure you can timely recognise (local) bird sounds so you do not chase them accidentally. You will enjoy your birding much more and get far more opportunities for good pictures. It definitely helps the birds to survive also.