If you ever find yourself not joining congregational prayer, take a moment to at least observe the people participating. You will find many unusual, unfortunate oddities consistently happening, regardless of where the prayer is taking place. Observe and learn, because you might be doing one of the following things yourself:
The politely-cloaked "You go ahead please": Even though the prayer has already started and the Imam is well into the second Surah, there is a standoff taking place somewhere in the back. This is between the people who don't want to move forward to a line closer to the front, but because there is a gap in the line ahead that needs to be filled, they offer other people the spot. They tell each other to go ahead as if they are giving the other a privilege, when they both know that neither of them really wants to move.
These people need to understand that moving ahead in the congregational rows will not cause one any physical pain or abnormal feelings. Having the motivation to move up as far as possible even increases the rewards of praying. People should just move up and quit causing distractions for others.
The Wave – Congregational Prayer Edition: In some quarters there is a misconception that one can only start their prayers once the person in the row in front of him or to his/her right or left side has begun. This ends up causing a lengthy, time consuming chain. People who are ready to pray are simply standing there waiting for their turn to start, even if the Imam is almost done with Surah Fatiha. FYI, as long as the rows are properly set, and the follower has heard the Imam start the prayer, (s)he can to start his/her prayer even if those in the front or on the side have not begun.
The Reckless Lane-Changer: A Reckless Lane-Changer is a person who was unable to join at the start of the prayer, but still wants to participate. When entering a highway, there are specific guidelines as to where, when, and how you are to merge onto it; you cannot simply swerve over when you wish! Likewise, when joining the congregational prayer which is underway, a person cannot join during Sujood, Tashahud, or just any other time that one sees fit.
If you are joining during the first rak'at, you can join anytime from Takbiratul Ehram up to the end of Ruku. If you join in the second or later rak'at, remember that you cannot finish your prayer with the congregation, as you will not have the sufficient number of rak'ats – a characteristic of...
...The Short-Changer: In this case you will have to carry on with your own prayer to complete the required number of rak'ats, after the congregational prayer has finished.
The Speeder: This is the guy who will attempt to complete certain actions quicker than everybody else. He will reach the position of Sujood faster than everyone else, or he will stand up for the Qiyam of the next rak'at faster than everyone else, regardless of the fact that they will finish the prayer at the same time as the congregation anyway. Reciting dhikr faster than the prayer leader is permissible. However, performing physical actions before the Imam does will invalidate your congregational prayer!
The Multi-tasker: This worshipper is interested in doing more than only offering prayers. Be it buttoning shirt sleeves, seeing if he have enough change in their pockets for a coffee, taking off a leather belt, strapping on the watch, or putting the cell phone on silent mode, Multi-tasker has a hard time focusing on what is only slightly most important – his prayer!
But these are also the ones who do not put their phones on silent mode, and then the ringing disturbs everyone. Although most will quickly shut the noise off, there seems to be the rare one here and there who will actually answer the call in the middle of prayer!
Hilarious to see, one more multi-tasking technique is to use the time during Qiyam to exercise the jaws. Because only the Imam is to recite the two surahs, some people think it's a good time to chew gum. Gum chewers: you can't eat food, drink drinks, or chew gum during prayer!
The Overly-Enthusiastic Reciter: Then there is that guy who enjoys reciting surahs out loud along with the Imam. Please note that the followers are not allowed to recite the surahs in the congregational prayer, either loudly or silently. Yes, if you can't hear the Imam at all, then you can recite the dhikr, but that also should be done silently.
The Tall Grass in the Wind: You might notice during Qiyam that some people constantly sway and swerve back and forth. If enough people are doing this, it forms a group known as Tall Grass in the Wind, which is basically what it looks like from afar.
The Physical Checkup: Oh yeah...remember the Multi-tasker? Another trait of his is to perform a physical checkup during prayer. During Qunoot, he finds it urgently pressing to check on the condition of the skin of his hands, and to see if his fingernails are clean or maybe in need of a good trim. During Ruku, he curls his toes and rolls his feet sideways to ensure a proper inspection of their soles or socks. During Tashahud, while the hands are conveniently placed on the thighs, some find this an opportune moment to brush away any small specks of lint or crumbs that may have gathered during prayer directly onto the person next to them.
So next time you do join a congregational prayer, remember that all of these things are wrong and should not be done. Extra movement should be kept to a minimum, as it distracts the person praying, as well as others around them. And most importantly, excessive non-prayer-oriented movement will invalidate a person's prayer. And none of us want that.