Don't let them take advantage of you. Let them know who's the boss.
Body language is everything. Act confident, don't give off nervous feelings. Be in charge.
Horsemanship (liberty work, join up)
Move their feet so basically groundwork and lungeing. Also if you want your horse to give you respect you need to give them respect too. 💙
Do lots of ground work take him/her to the arena and practice stoping when you stop and if he/ she doesn't make him/her back up a few steps and repeat. But also if your horse is not responding or being lazy make him/her trot a few strides and walk and repeat this teach the horse that if he/she doesn't respond to what you want work will be involved.