Combat reflexes is the obvious choice. we have a Cleric Lizard man in our group with a spear and combat reflexes. in one encounter he killed 4 out of the 6 Grippli in one turn just due to them moving through threatened area. it was awesome.
You need to focus as a cleric to do anything much of consequence, otherwise you end up a buffer and healer. Building a reach cleric means focusing on attacks of opportunity to do your damage. You need a very high dex, and feats to further expand your reach. A good thing is that you get to keep your normal actions in the round for whatever you like, so buffing is easy, optimally you want things that make you bigger and stronger. You also need to optimize your to hit, meaning a high strength, otherwise you will be good for a few levels, then all your attacks won't mean much. You must also get your damage up by some convenient means, whether through equipment, strength, buffs, or feats. All this means you really have little wiggle room when it comes to your other attributes. Wisdom needs to be decent to let you cast your buffs, but the feats involved mean you aren't going to be a good blaster or summoner or the like. Shelyn is a good deity for reach builds, because the favoured weapon is glaive.
However! A longspear is a perfectly respectable weapon.
True, usually, the difference between that and a glaive would just be 1 average damage.
Take the better weapon if it is readily available (ie- you have martial proficiency, and you can freely choose between weapons) but don't bother losing anything too major over it (ie- Desna's absurdly good domains). Reach alone is mostly enough to cover your problems.