The Rebbe's guidance to those struggling to find a shidduch is consistent across many letters:
Actively search; don't wait. Finding one's match is compared to searching for a lost object: a person doesn't sit and wait for it to turn up. Make use of friends, family and shadchanim, and don't delay, since every day of delay is a real loss (IK 1694, 3211, 3312, 4006).
Don't overanalyze. Look at the essentials: yiras Shamayim, Torah and mitzvos, and good middos. Don't reject a suggestion over minor flaws or status differences. Move forward with trust, like Nachshon stepping into the sea (IK 2523, 4895, 4980, 5946, 9468).
Bitachon and simcha. Keep away from sadness and worry, and trust in Hashem even when it seems impossible by natural means (IK 2051, 3220).
Strengthen the spiritual channels for the bracha: check tefillin, give tzedakah daily, say Tehillim, and set times for Torah study. Don't rely on segulos from various books; go with simplicity and faith (IK 2051, 5974, 7377, 7692, 8740).