1). Before working in the lab, read carefully the Vogel’s Textbook of Practical Chemistry (e.g. 5th Edition)-Chapter: Reactions involving replacement of the diazo group (bromo-, dibromo-, tribromobenzene).
2). Work in the lab hood and shut the protective screen.
3). Wear protective eye-glasses.
4). The temperature must not exceed 0-5oC during nitrite addition and 10oC during the reaction, except if otherwise written in the Vogel's Textbook.
5). Keep a spare amount of ice for cooling until the end of the reaction; you may need it if the reaction gets vigorous.