Here's a scaffolded, step-by-step PPT that is great for direct instruction on how to add and subtract rational expressions. It starts with a warm-up that requires students to add regular fractions, then goes into adding and subtracting rational expressions both with like and unlike denominators. Each example is fully explained and written out. Students will have an opportunity to create least common multiples for rational expressions with different denominators. Classwork is included from the Holt-McDougal Alg 2 textbook. An online YouTube tutorial is also embedded in the PowerPoint, which I found really helped my kids as a "preview" to the lesson this year.