When you write your argument "in favor of religion", consider potential objections that this forum is likely to offer, steelman them, then counter them the best you can, using the language of the forum, then repeat. Basically, try to minimize the odds of a valid (from the forum's point of view) objection not being already addressed in your post. You are not likely to succeed completely, unless you are smarter than the collective intelligence of LW (not even Eliezer is that smart). But it goes a long way toward presenting a good case. The mindset should be "how would DSimoon/Desrtopa/TheOtherDave/... likely reply after reading what I write?". Now, this is very hard, much harder than what most people here usually do, which is to present their idea and let others critique it. But if you can do that, you are well on your way to doing the impossible, which is basically what you have to do to convince people here that your arguments in favor of theism have merit.
EDIT: When you think you are done, read Common Sense Atheism for Christians and see if you did your best to address every argument there to the author's (not your) satisfaction and clearly state the basis for the disagreement where you think no agreement is possible. Asking someone here for a feedback on your draft might also be a good idea.
steelman
This terminology would probably be obscure to a newcomer. For ibidem (and any confused others), here's the explanation, on the Less Wrong wiki.
A few notes about the site mechanics
A few notes about the community
If English is not your first language, don't let that make you afraid to post or comment. You can get English help on Discussion- or Main-level posts by sending a PM to one of the following users (use the "send message" link on the upper right of their user page). Either put the text of the post in the PM, or just say that you'd like English help and you'll get a response with an email address.
* Normal_Anomaly
* Randaly
* shokwave
* Barry Cotter
A note for theists: you will find the Less Wrong community to be predominantly atheist, though not completely so, and most of us are genuinely respectful of religious people who keep the usual community norms. It's worth saying that we might think religion is off-topic in some places where you think it's on-topic, so be thoughtful about where and how you start explicitly talking about it; some of us are happy to talk about religion, some of us aren't interested. Bear in mind that many of us really, truly have given full consideration to theistic claims and found them to be false, so starting with the most common arguments is pretty likely just to annoy people. Anyhow, it's absolutely OK to mention that you're religious in your welcome post and to invite a discussion there.
A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site!
Note from orthonormal: MBlume and other contributors wrote the original version of this welcome post, and I've edited it a fair bit. If there's anything I should add or update on this post (especially broken links), please send me a private message—I may not notice a comment on the post. Finally, once this gets past 500 comments, anyone is welcome to copy and edit this intro to start the next welcome thread.