There is one thing to know before starting any lawn treatment plan. Unless you are going all in for year round treatments done waist money on just doing one or two treatments a year. With so many weather changes through out the year and certain weeds that come up at specific times in the year, completing only one weed treatment in the spring can be undone if you done treat them the rest of the year. This goes for fertilization also.
Knowing that above it does not mean you have to go with every treatment on the market all year every year. The goal for any turf program should be asses the lawn to identify the issues, come up with the plan to fix them and then monitor the results to make adjustments. Plans can be as basic as four treatments a year or as much as 7 treatments while adding lime and moss treatments along the way.
Always know what to expect when starting a new lawn treatment plan for the first time or switching from a previous service provider. Unless the lawn is in fantastic condition do not expect to do a 180 with in the first couple treatments. You should expect to see results moving in the right direction but the chemicals used are made to fix things over the long run. Depending on the condition of your yard it could take up to two years to get a final product of a great lawn.