Easiest way to do this I've found - Changeling Factotum/Chameleon - be anyone in anyone's dream, make sure to have a greater armor crystal to protect yourself from the dream heart.
Or abuse the items don't get used in the dream rule and be an artificer with the apprentice feat to gain the class skill, make scrolls, wands, and potions galore for use in the dream.
Gather information - spy on their dreams and use the change one thing in the dream to bring into play subjects you want to know about
Diplomacy - gain their trust through long conversations so when they meet you they start as neutral or friendly.
Seduce the wife/love interest of your target - get them to fall in love with you and betray their current interest at an opportune time.
Intimidate the target - use fear and danger to make the target afraid to sleep or kill them outside the dream heart to force them to wake up, especially effective with spell casters if you can prevent them from getting 8 hours of rest. (Only used on targets you don't want to really kill)
If you used the Apprentice feat to gain the class skill - Train with your Master/Apprentice - 1 min real time = 10 min dream time
Go deeper
- put the target to sleep, and then follow them into their deeper dream for more crazy shenanigans!
Depending on how real your DM makes the Dream Heart- use the change the dream check to create an item, then put it into your haversack before you wake up.