Specific
“When I have time” is too ambiguous. Make it specific, like “everyday after dinner”.
Measurable
“Some books” can mean two books or three books. It’s better to change “some books” into a measurable number, say “3 books”.
Achievable
When the goal is too ambitious for us to achieve, we may get frustrated and lose the motivation to go for it. For example, “finishing one book a night” might be too difficult, so please set the goal to “one chapter a night” first.
Relevant
The goal should matter to you, be at the right time and aligned with higher goals. For example, I’m going to read this Japanese book so my Japanese will improve and eventually I can enjoy Japanese dramas like a local.
Timebound
Give a time-frame for finishing this goal. Example: one hour, one week, or one month, etc.