
I am assuming that your bitch comes from a knowledgeable breeder, who is the best person to tell you if she is good enopugh to be bred from, and that you have had her Hip Scored and eye tested with good results.
A large dog like a Labrador should be at least two years of age before being bred from, and in practice is likely to be nearer three depending on spaving of seasons.
Bitches can vary greatly with the length of time between seasons. A normal season interval can be anything from 4 to 12 months apart, with an averge of around 7 months, so she should be about due in the next month.
Some bitches show very little bleeding (I hae two like that) but there are little clues that they are coming in shortly. Usually they will squat to pee more frequently on walks. Just before the season the vulva will be starting to swell, and if you fel above it belwo the anus the are will usually fel a bit hardened.
At this point I dab the vulva twice daily with white tissue, and count day one from when I first get colour (blood).
To get an idea of what suitable dogs there are around I would attend shows, and see which dogs are producing the type of offspring you admire (especially if the mothers are related to your bitch). As a Novice it is best to work with an experienced breeder to advise you, as they will know the dogs in your bitch's pedigree, and if knowledgeable witll know their failings and strong points, so that when choosing a mate for yoru girl you will not be as likely to fix her faults, and hopefully enhance her good points.
You should also consider that it will cost you in the region of £1500 to breed a litter, what with health tests, equipment and rearing costs, and that is withour problems during whelping. If your reason for breeding is primartly to keep a pup for yourself, then it will be far cheaper to just buy one from your bitches breeders next litter. Remeber once born you will ahve a lifelong responsibility for the pusp produced, and may have to take back more than one of them at any time in their lives for rehoming. They usually come back because they are naughty, and having to rehabilitate an adolescent of Labrador proportions is not a task for the fain of heart. Will you have the time and room to do this?
Even now that I am more expereinced with homing my pups I still on average have one pup in a litter come back at some point, anything from 5 months to 4 years so far.