Hi martingale:
You will find a range of recommendations on what/what not to do here. I would offer that you gather as much local information to Maryland and your growing conditions (soils, temperature, rainfall, etc.) that you can. Maryland is a quite diverse state regarding soils, elevation, moisture regimes, etc. Your County Cooperative Extension Service office will have a lot of literature and local knowledgeable people to help. Once you have consumed that ("so much to know" is exactly right), then come back here if there are things that you like further explained.
As noted previously, there are many vigorous "winter" or "cool season" annual weeds that will already have finished their bloom cycle and set seed - like that Chickweed. Spraying it with some sort of chemical will certainly kill what is left of it, but as a seasonal weed it is dying anyway and it will not eliminate the seeds that have already been formed and have probably dropped to the ground as well. Gathering the foliage and stems and composting them or disposing of them otherwise will help to some extent, but you will have new seedlings come winter. Recognizing the plant as it starts growing is the key, and then dealing with it before flowering/seeding helps set you on the path to reduction or elimination.
Also noted, the various clovers do provide some level of value to soils with poor structure or deficient in nutrients - but nowhere is it stated or known whether your property is afflicted with either of those ailments. Again, a visit to your Cooperative Extension Service office can gain some recommendations about evaluating your soils and landscape for a variety of baseline information. Armed with this data, you can make more informed and directed choices to improve your growing conditions - for lawn grasses as well as other aspects of your landscape.
Come back here often for plant ID and other information - but raise your overall knowledge so that you can better answer the inevitable questions that will volley forth from here.
