Frequently reoccurring svn task is: add an existing source tree as a new project in a svn-repository. Here's how I do it:

# done once and for all, this creates a template I use for all my svn-projects
mkdir ~/svn/project_template
mkdir ~/svn/project_template/trunk
mkdir ~/svn/project_template/tags
mkdir ~/svn/project_template/branches

# done only if you want a new repository (which may contain several projects) 
svnadmin create /path/to/repository 

# next, create a new empty project, called NewProject, by importing the template:
svn import -m "new app" ~/svn/project_template file:///path/to/repository/NewProject 

# Next, cd to the parent of the new source directry, i.e. 'NewSourceDir' below should contain
# all files and directories you want to add to the trunk-directory of the svn-project. Next do:
svn co file:///path/to/repository/NewProject/trunk NewSourceDir 
# this turns the NewSourceDir to working copy of trunk,
# but it doesn't add any of its content.
# So now it is time to start adding the stuff:
cd NewSourceDir
svn add X Y ...
# and finally a commit:
svn ci

This is my preferred way of doing it since it lets me add the new stuff selectively. Rather than using 'svn import' to add everything at once, in which case I would first have to create a 'clean' copy of the new source. Hmm, i'm gonna put the above in a script so that I don't ever have to look at this post again :)

Just a note on svn add. Default when add is applied to a directory is to add all its content recursively. To add only part of the content, use the --depth flag. That is:

svn add --depth=empty NewDir

adds an empty NewDir to the reporitory.

svn add --depth=files NewDir

adds NewDir and all files it contains, but leaves out directories.

svn add --depth=immediates NewDir

adds NewDir and all files and directories it contains, but not recursively.

Here's a link to another svn cheatsheet which covers some other tasks.