Writing is hard work, and anyone who says otherwise probably hasn't written much. Some learners really enjoy it, but most find it a grind. Like any other skill worth having, it takes time and patience to perfect. As your learners become more proficient at it, they'll be looking at different techniques like building lists of word substitutions to enhance their craft.
This infographic below from GrammarCheck, 16 Boring Words & What to Use Instead, is a practical place to start. It features a list of 16 of the most basic and mundane words found in writing of all sorts, followed by a handful of interesting substitutions for each one. Your learners can keep this list handy along with others as a go-to resource for using word substitutions to replace some of these terms in their own work.
Using substitutions for commonly overused and uninteresting words is a simple way to spruce up writing, but it must be done with care. It takes practice to match any potential word substitutions with the overall tone of the content. Writing is one of those practices in which there are so many little things to consider, and this is definitely worth their attention.
Encourage your students to constantly ask themselves questions like these as they experiment with word substitutions:
Writing is a personal and introspective craft, but even so there are always the needs and expectations of the reader to consider. In using word substitutions effectively, your students will learn to not only challenge themselves, but their audiences as well.