Any general guide on Taxonomy will help. You'd be surprised how many plant names are a direct reference to their identifying features. You basically just need to know the latin words for colors and shapes to narrow your search. With a Biology background, you likely have a good general knowledge of latin, but a reference is still helpful.
The next thing is to learn the characteristics (leaf shape & placement, stem type etc)
http://www.clemson.edu/extension/natural_resources/landowner/youth_environ_education/terminology.htmlField books are sometimes useless. Many plants have been renamed or completely reclassified in recent years, so books can go out of date. For example, the move of common meadowsweet from Spirea to Filipendula, or the constant reshuffling of bamboo species... A smartphone is a much better tool. It's up to date and much more portable in the field (plus has navigation tools and other useful apps for that type of work). Try the following websites:
https://gobotany.newenglandwild.org/full/http://plants.usda.gov/java/Additionally, look up wild plants native to your area (your region's Environmental Conservation Dept should have an extensive list). Your local ag extension will also have lists of native plants. If you strike out with the guides, a phone lets you take a picture and post it online for others to help ID.
Like any taxonomy, just learn the general characteristics which define a plant family. Individual species can be harder to determine (some are very obvious, many are not) and the cultivars may be nearly indistinguishable visibly, you need to see them over time as they grow to understand growth characteristics. Focus on the plant families. After a few hours of reading, you should be able to correctly place most plants in a family with ease. Here's a nice guide to common plant families:
http://www.sci.sdsu.edu/plants/plantsystematics/Identifying_50_major_plant_families.pdfFocus on Lamiaceae, Rosaceae, Asteraceae, Boraginaceae & Fabaceae. That'll make up most of your garden plants and common useful weeds. These are
huge families.