The more time you spend talking, the better things will get.
However, I've been using a Kindergarten Vocabulary curriculum with my 3 year old. It probably too advanced for where you'll be in the next year, but you may want to look into it for the future. It is all picture based and focuses on age appropriate words for things that a preschooler can grasp. It even covers some words multiple meanings. Wordly Wise 3000 from Educator's Publishing System (EPS): They have books for K-12. K and 1 need the teacher's manual for stories, poems, and the picture cards that go with the workbook. It's great and only takes 10 minutes a day to master 120 words in a year. It's about $80 each for K and 1 and about $12 for 2-12. It's well worth the cost. I've seen my son's vocabulary soar. We also got to the library and read easy science books on topics from our vocabulary stories. We've read about plants, water, deer, owls, rabbits, and more.
Also consider going to story time at the library. It's great and will expose your little one to all sorts of new books and concepts you can narrate and/or read to him about.
READ, READ, READ!