Teaching a pup to walk on a leash is a vey hard thing to do. Every pup I've had just hated it. It takes a lot of practice and probably going to take some bribery.
You cant start with just getting him use to wearing the harness around the house while he is sleeping, playing and eating. Also start teaching him the Come command which will come in handy for walking and stopping once you do get ready for a walk out doors. Once you feel he is adjusting to the harness, once or twice a week work with him in the house with his leash on. Be sure to praise him every step of the way and it wouldn't hurt to reward him with a Cheerio every now and than. Cheerios are great for training, not too filling at all.