Multiclassing for fighter levels is a good idea, but to really make a good magic & melee cleric it's not nessessery to take too many. You will have to choose a combat feat chain to focus on (Power Attack -> Cleave -> Great Cleave, for instance. Or Weapon Focus -> Weapon Specialzation, Improved Critical). Take a fighter level at 1st or 2nd, in order to get quick acess to martial weapons, and limit yourself to 1, 2 or 4 fighter levels. These are the best break-points for power, and won't huet your spellcasting too much if spaced out. (1 or 2 levels is good if you just want to get your basic feats sooner, a slight BAB boost. Four is good if you want weapon specaization, or if you want a more significant BAB bonus).
For most spell casters, particuarly multiclass ones, meta-magic feats become more usefull at higher levels. So early on you can focus on either augmenting your combat abilities with more feats (a second chain), or a few item creation feats. Later you can mix and mach as you wish. The most usefull meta-magic feats for a cleric are generaly Extend Spell (and, if you can get it even though it's FR, Persistant Spell is a wonderfully imbalanced feat once you're high enugh level to cast a persistant Weapon of the Deity (DotF) or Divine Might. This won't be until you're a 17th level cleric, though, and is going to cost you 8th level spell slots).
Good item creation feats are Scribe Scroll (Have any spell you'll ever need potentialy on hand, make extra healing scrolls that you or anyone with Use Magic Devices or very basic divine spell-casting skills can use), Brew Potion (More limited in effect, dosn't allow the high level or many powerful offensive/utility options of srcolls, but spreads the healing around better & are a bit cheeper), Craft Wand (All the combat / healing spells you'll need for a while, as long as their low level. Wands of Cure Light Wounds never go out of style, having a near unlimited resource of Searing Light or Poison is very handy), Craft Arms & Armor and Craft Wonderous Item. Unfortunately your domains don't allow the nicest abusable element of craft wand (letting you use powerful arcane spells much more often than once per day, there simply arn't any good ones in either domain before 6th level, compaired to Trickery or Travel, for instance) but if you're willing to take craft Staff you could at a fairly high cost (buff up everyone with stone-skin, if you need to).
Good prestige classes depend on party makup... If you look at a class that dosn't augment your existing spell-casting class like the Templar or Hunter of the Dead then focus on cleric levels (perhaps even ignoring fighter levels) until you can get the pre-reques, then multi into that instead of fighter. If you want something that only partilay augments your existing cleric spell casting (War Preists are GREAT when you have a larger party) you'd also want to focus mostly on cleric. The idea is not to water down your spell-casting too much. Rely on Divine Favor in important fights to make up the BAB diffrence.
Later on in life you'll have to make a choice. There are many, many good higher level cleric spells. But you only have so many rounds in each combat, and if you just keep casting you'll loose your chance to get into melee (and thus make a lot of your feat choices less than usefull). You can either abandon the cleric levels once you have a good handle on spell-casting, or you can take meta-magic feats like Empower and Extend and primarly use meta-magiced, long duration spells before a fight to augment yourself and your party, with just the occoinal Flame Strike or Heal on your spell-list for bad situations. The latter is more flexible, though the former may be very instering with the right feats & a prestige class or two.