The beginning of any relationship starts with that first glance. It builds on communication and touch. Your relationship with your dog is no different.
Observation.
Whether you are building a relationship with your foster, adopted, short-term or forever - dog, it is important to not impose yourself and your wishes upon them but first sit back and observe them in a controlled and safe space. Here are a few things to look for:
Are they comfortable on the surfaces?
Do they go toward or away from stimuli?
Do they greet you or feel more comfortable at a distance?
Are they food motivated?
Are they interested in play?
How do they react to other dogs?
After this period of observation you will have a good sense for how confident your dog is and some areas where you may need to focus training.
Connection.
On the most basic level, your goal is to be viewed positively by your dog. From this positive perspective, your dog will be responsive to your behaviors, cues and requests. A simple way to build this rapport is through food. It is a basic need you provide your dog and with it, you can reinforce how you are a benefit to your dog. Plain and simple.
I recommend carrying treats in your pocket or treat bag for the first few days, if not weeks. The access to food anytime your dog is caught doing a behavior you want to reinforce will allow you to accelerate your connection and positive behaviors.
Games.
Name-Game.
Say the dog's name near them. When they give you attention - a look, coming to you, sitting, etc give them a treat. Start with a loose definition of success and slowly narrow it. At first coming anywhere near you would earn a treat. Eventually, you will withhold the treat until they improve upon that. (This is known as shaping behavior.) This may mean that they make eye contact, allow you to touch them, allow you to touch their collar, sit at your feet etc. Through this game you're building name awareness as well as a comfort in your proximity to them.
Yes-Game.
When your dog is doing any desirable behavior, regardless of what it is, say yes and give them a treat. The goal in this early stage of rapport building and training is not to train specific behaviors. In this game your goal is to teach them the word yes equals good. They already feel food is good/beneficial so we want to teach them that the word yes also means good. Yes, is a word that you can use anywhere without limitations. This is a very similar concept to clicker training but replacing the clicker with the word, yes.
Make note of what your relationship is like today and how it is different after practicing these games for the week.
When play is work, work is play.