If you read, read, read and study the way various authors make characters come to life on the page you will see that working both with the five senses and internal thoughts can really help. My advice is to read the character descriptions in the books you love and to especially pay attention to how they speak and what they say as that is what shapes people’s impressions of us and therefore readers’ impressions of characters.
Most importantly, pick an amount of time each day, 30 mins, 1 hour, and sit down and DO IT.