There is nothing more rewarding than helping an animal move from a shelter into a home. Usually it prevents them from being euthanized and gives them that chance they otherwise wouldn't have had. It comes with a lot of responsibility and often a lot of work on your part. The animal goes through many changes and emotional states. I am not going to say I know all about it, but I have seen some great fosters do amazing things and given so much to so many of these babies.
Before you commit to taking one from a shelter please consider the length of time at which you will be able to hold on to them. If you are assisting a rescue and know that 2 weeks or 1 month is the tops you can do, be up front. It will prevent you from being able to foster but will help them better organize. They may have one going to a new home in 2 weeks but another they are watching in a shelter that is on death row. They can utilize your two weeks by moving that one from current foster to you until the adoption or transfer is complete and move the animal on death row from shelter to the foster that is able to hold with unlimited time. Be up front and honest with yourself and the rescue. It makes things go so much easier. Rescues, especially in Texas have a difficult time finding fosters so it puts them in a bind when someone decides all of a sudden that the animal can't stay.
Do some research on what dogs go through as they transition from Shelter to Home and how to properly introduce to new animals. Dogs tails are how they can speak to you. It is something I am still learning and find it rather fascinating. Dogs should never be introduced nose to nose as it can cause them to get the wrong impression.
Gather as much information as you can about a dog before committing to take it in. Shelter staff will usually answer any questions you have or let you know if they can't find out. What sort of questions do you ask? Are they good with kids, cats or other dogs? Do they act differently with men than women? How do they act differently? Have they been abused, neglected or mistreated? That can play a huge role on how they react to you. You can reach down to pet their heads and they may sink away to the floor or stand ready to defend themselves. These kinds of dogs are not aggressive, they are just insecure and need a lot of love, patience and slow movements until they come to trust you and know they are safe with you. It's also best to do slow introductions to new people they meet, any friends, family and neighbors may make them uncomfortable to insecure. It is best to put them in a quiet room where they are separated for large parties so you don't have to worry about their fear and they can feel safe. If it is just one or two people, have them sit and be still for a second while the dog approaches them to check them out. Have them move slowly to pet or reassure them they are safe. You, as the foster or new owner should never leave the dogs side as they know and trust you. Please consider limiting introductions until they do know and trust you.
All of them need a decompression time where they can rest, get use to their new environment, sites and sounds. They may be perfectly happy and friendly right off the bat, depending on their history or they may be quiet and withdrawn for a week or two, some longer. In the end, it is very rewarding to give them a safe place to be and teaching them that not all humans are evil or aggressive but most of us are kind and loving.
Getting a dog from a rescue is more expensive than getting one from a shelter but can also be helpful. We do take the time to get answers to any questions. Unlike a shelter we are able to put them into certain situations to see how they react....just don't ask us to put one in a situation that would be dangerous to them because we will not do that of course. Reach out to local rescues, talk to your local shelters and make sure that the pet you are planning to adopt because they are pretty, is a good fit. If not, keep looking. Don't grab and dump. In the end, that just scars them more. Always consider professional training. Most rescues work on training for their pets and find outside professional training when it is necessary.
Whatever you do, do not make the decision lightly or quickly. Take the time to do some research, ask questions and get answers, set up meet and greets or whatever else you know that may be needed to ensure the pet you take home is forever home.
We highly recommend that you visit https://www.cesarsway.com/ and read any books or watch videos by Cesar Millan. Cesar Millan's Short Guide to a Happy Dog is an excellent read.