Losing Strategies
Gank the Other Realm's Spawn Objective:
Occasionally, one team will send 1 or 2 people to the opposing realm's spawn objective to try and get a sneaky capture. This strategy might seem to work at first, and may seem very appealing. But in practice this only accomplishes two things:
Virtually guarantees a loss at the Fort since your team will be outnumbered. The Fort is worth double the capture points of the Barracks or the Lighthouse, so this is a net loss of 15 points.
The opposing team will almost certainly capture it right back when their respawns roll through and probably outnumber whoever capturedit. This gives 15 points to the other team, which nullifies the initial capture points. So now you have a net loss of 30 points.
Worst Case Scenario: A couple members of your team run across to capture their spawn objective. They flip it from controlled to uncontrolled, but soon after get killed by respawns or nearby enemies. The enemy then recaptures it for themselves. During this time, the enemy also takes the Fort due to their numerical advantage. This results in a net loss of 45 points (30 points for the Fort, 15 points for recapturing their spawn objective, and none for your team). This also means the opposing realm got 60 or so points for kills (since they probably killed all 12 of your team), and due to being outnumbered your realm may very likely have received 0 kills. So within the first couple minutes of the scenario, your realm is already down 120 to 0. Brutal.
Nothing Else Matters... GET THE FORT!
This has been addressed elsewhere, but it bears specific mention as a losing strategy. Throwing yourselves repeatedly at the fort will accomplish nothing but give the other realm a lot of easy, fast points, renown, and experience. This is particularly true if subsequent attacks on the Fort happen haphazardly as your fallen allies straggle in after various respawns. This strategy frequently degenerates into fighting half way between your own spawn objective and the Fort. This means you never even threaten the Fort in a serious way, and they enemy just farms you at their leisure.
Things to Avoid
Yelling "HEAL!" or other criticisms of the healers. While it is possible the healers on your team are bad, one or more of the following is more likely:
1) They are overwhelmed. You might have too few healers, or their level may be such that there is not much more they can do.
2) They are constantly under attack and/or nobody is helping them shed attackers.
3) You simply charged ahead foolishly, got focus fired, and were out of healing range or (rightly) deemed not worth healing due to your own recklessness.
4) The other team is simply better. If the other team is delivering ferocious DPS, your healers will simply be unable to keep up.
Insist that the only way to win is to hold the Fort. I think this has been addressed sufficiently, but it really needs to be driven home.
Calling your teammates stupid, noobs, fools, or any other insult. Tier 1 is a chance to get to know people on your realm. These are people you may be fighting with for many months or years to come. They may be learning how to play MMOs for the first time, or learning a new class archetype. No matter how badly you think they are playing, these are your teammates for now and perhaps for the future. Helping them learn is a much better idea than criticizing them for failure. Furthermore, the failure may be your own and not theirs. In RvR based games, your reputation is more important than on purely PvE games. Being liked simply by 25-40 people in your guild that you raid with is not enough. You will need to be able to work with hundreds of different people if you have any hope of success in large, open world RvR.