Steps

1. Assume the DATADIR is /usr/share
2. Copy ${DATADIR}/ibus-table/tables/template.txt for the template to begin with. Assume it is your-im-table.txt
3. Make an icon for your im, assume it is your-im-table.svg.
4. Edit the your-im-table.txt to suit your need.
5. Fill the actual table content between BEGIN_TABlE and END_TABlE.
1. The 1st field is "Input Key": the key sequence to produce the word/phrase
2. The 2nd field is "Phrase": Word/phrase to be produced.
3. The 3rd field is "Frequency": The usage frequency of that phrase. Phrases with more frequency will be in front of candidate list.
6. Install ibus-table if you have not.
7. Run

ibus-table-create -n ${DATADIR}/your-im-table.db -s your-im.table.txt
cp your-im-table.svg ${DATADIR}/ibus-table/icons

8. Restart ibus-daemon.
9. Enjoy your input method. :-)

For input method developers

It is recommended to split database building and index creating, as it makes distro packagers' life easier.

Use -o option of ibus-table-create to build database without creating index; use -i option of ibus-table-create to create index without building database.

For packagers

Install the database file which is built by ibus-table-create -o, and create index with ibus-table-create -i in your post-install script script.