Mary,
A lot of cameras, including the Canon Rebel series, are designed to make a lot of photography easier for the user. But when you start trying to get the best photos from trying situations you have to move from the "easy button" to making educated decisions for the best setup.
Soccer was the sports photography start for me and I started when I was also coaching 6-7 year old kids and stayed with it as my daughter moved up through the ranks and into high school so I definitely had on the job training.
To add to the suggestions you have already gotten, here is what I have learned from about 15 years using various camera and lens systems over a variety of sports.
1. Always shoot in RAW because not only does it avoid the issue of getting white balance correct at the time of exposure as pointed out by ebiggs, RAW files also give you the greatest latitude for recovering from exposure issues which is common in sports. Most cameras will slow down processing when they have to create both RAW and JPG files so just choose RAW for output and you can create all the JPG files you want during post.
2. Location is critical and you want to be as close as practical, avoid having the players heavily lighted from behind, and have a field of view that isn't blocked frequently by sidelines, coaches, officials, etc. I am fortunate with the high school team to have sort of diplomatic cover because I coached many of the players when they were coming up and I have known them and the high school coach for years so I can be on the sidelines. But part of this is because I coached I know when to stay out of the way of the coaches and officials. As you know soccer moves very quickly and you don't want to get hit by a player or a ball risking injury to you and the players. And the game officials will take a very dim view if you crowd the sideline.
2a. Soccer is perhaps the hardest field sport to shoot because the field is huge and the action is extremely fast in moving from one part of the field to another and it doesn't stop between plays like U.S. rules football. There is no optimal place to cover the entire field optimally and I move around some during the game to feature certain players and plays. Generally you want to capture the play moving towards you but for your team's defenders and keeper you will want photos of the opposing forwards and mids driving away from you and towards your keeper. Just like the coaches have a game plan, you need one also to get the coverage you desire. All of this means the importance of location is even more difficult to put into practice with soccer.
3. I shoot almost every game in manual and if radically different lighting around the playing area demands it I will set ISO to auto. Most of the time you will have your lens set wide open (F stop set to lowest value which is the widest aperture). For youth soccer, you can go as low as 1/500 shutter speed and get a lot of nice shots with little or no motion blur. For high school and above I prefer 1/1000 minimum and will go higher if lighting allows but if necessary even at the high school and above level 1/500 will produce a lot of nice shots if your lens and lighting situation demand the slower shutter speed.
Most of your shooting will be with your 55-250MM and I would set the F stop to its lowest value and keep it there. Using a combination of the lowest F stop and 1/1000 shutter speed, see what ISO is required to get the standard (proper) exposure. If the ISO is too high to provide good results (low enough noise) with your camera then drop the shutter speed. Going from 1/1000 to 1/500 is a full stop in shutter speed which means you can also then drop a full stop in ISO (i.e. from 3200 to 1600).
4. I am not familiar with the AF setup of the T5i but in general you will want AI servo mode so it will follow movement and I would choose either the exact center focal point or the point vertically above that one for shooting action. This helps you control what the focus system will choose and for many camera bodies forcing it to use a single point rather than allowing it to select which point to use during a play will result in faster focus acquisition. It does take some practice to keep that single point where it needs to be but it is one of the techniques you will have to use to increase the percentages of good shots.
5. Select continuous drive mode so that when you need to you can fire a sequence of shots but do NOT get in the bad habit of relying upon using it as a crutch. You still need to anticipate the proper time to start taking images and if you just "pray and spray" with the shutter button you will miss a lot of good stuff because your camera will slow down as it processes a lot of "garbage" images while you miss the next good stuff. Consciously force yourself to do a quick press and release so that you only trigger a single exposure when you want in continuous drive mode. I have my 1DX 2 set for 14 FPS shooting but a lot of the game photos I take are just a single image via a single fast full depression of the shutter release.
Over use of just holding the button down will also greatly increase your workload after the game as you have to sort through a lot of useless images increasing the likelihood that you will overlook a good capture. You still will have a fairly low percentage of "keepers" and that is the nature of the beast in shooting sports but smart camera management will greatly increase that rate while decreasing the odds of missing some truly great opportunities. One of the easiest players to photograph in soccer is the keeper since he/she is more confined to a certain part of the field. Once you know the keeper, watch his/her face through the viewfinder and you will know when they are about to execute a stop or save via their expression and particularly the eyes. At the other extreme, headers are impressive and often difficult to capture because you are forecasting the trajectory of the ball and players, often on a windy day. If you want these kind of shots, some players are "header magnets" so track them using AI servo and keep them in frame when a keeper is sending the ball downfield or you suspect one will try to score with a header off of a corner kick.
6. It will get easier as you go through the season and learn the players' styles so that you can often predict where the action will move. The coaching staff well knows the tendencies of their different players and if you get to know them and approach them at the proper time (NEVER right before OR during a game) then they may be willing to give you some tips about what to watch. But remember you are a guest and the officials and coaches are the rulers so make sure not to get in the way and remain situationally aware. During one high school game I shot during the Fall, I was using a 300MM F2.8 with a 1.4X extender which provides a nice telephoto view of the action but it is also a physically long lens. I made very sure never to have the camera anywhere close to getting in the way of the side officials who stay ahead of the play and often have to run up and down the sideline. A parent of one of the opposing team members actually forced the official to run around her a couple of times during the first half and she lost her privileges to shoot near the sidelines for the second half. You are there to document but never become part of the action; it is both a issue of safety and and issue of respect for the game and its participants.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
, if you shoot Raw format and use a good post editor you can forget the WB settings. It is easily set in post.
