Don't hesitate to signal when you get cold and want to end the dive, or if you are having any other problem like equalizing. Sometimes newer divers are reluctant to slow down or call a dive with a more experienced buddy (although I think this is probably more of a male thing,) that is a mistake to avoid.
If it's a low vis lake, stay very close to your buddy at all times and be sure to review - and if necessary to use it stick to - your contingency plan for buddy separation (1 minute search, then slow, safe ascent to look for each other on the surface.)
