When it comes to ice safety, I have one simple rule to follow: “When in doubt, don’t go out!” 
Always be sure to inquire about ice thickness before venturing out onto any frozen surface. Local authorities, Department of Natural Resource Offices, Fish and Game Departments, local snowmobile clubs, various fishing club members, sporting goods stores and bait shops or outlets are all good sources of reliable information. Generally, a minimum of 3-4” of solid, clear blue ice is recommended for walking.
If you are walking out for the first time, always travel in pairs and stay several yards apart. I strongly recommend using an ice chisel such as HT’s HTIC-1 or HTIC-2 to chip the ice in front of you to check the ice. For a variety of reasons, ice does not typically freeze uniformly, and by punching the chisel in front of you, you may help avoid an unexpected, frigid plunge.
I would also urge anyone traveling on unknown ice for the first time to carry a rope and a set of safety picks, such as HT’s PL-10 or PLD-10 safety picks. In the event you actually do fall through, you can tie the rope around your waist and toss the other end to your partner. Safety picks can be used to help pull yourself back onto solid ice while your partner helps lift you to safety.