Is he a STR/WIS melee Cleric or a WIS/CHA "laser" Cleric? His stat array makes a difference in how to help.
For a STR cleric I'd say get light/heavy shield and start with at least a 13 CON (dwarf with an 11 + 2 is good here) so you can pick up Scale and by level 21 (with 11/21 stat bumps) you can finally get plate.
For the WIS cleric it's more stat dependent and without knowing how he allocated it's hard to say. IMO the "laser" Cleric has MAD issues as regards defenses. Either you accept that he's gonna get hit more often, or you sacrifice your to-hit in order to pick up STR/CON so you can get scale and a heavy shield. Either way you're going to have problems. I've also seen suggested an Elf Cleric starting with a 16/16 -> 18/18 WIS/DEX. This can give you a 17 AC (with Hide) at 1st level and a decent to-hit as well as being able to use a longbow ranged basic attack, or you can try to squeeze a 13 STR in there for a shield and have a 20 AC by level 2.
As for him not hitting well that also depends a lot on his stats. Expertise is good for anyone needing to hit. For the STR cleric I advise picking up any +3 weapon proficiency (long sword, bastard sword) because for a Cleric it's more about getting the buffs than the damage he does. For the WIS "laser" Cleric there's not much more to do than start with an 18/14/11 array and put the 18 in WIS and be sure to pick a race that bumps WIS to 20. You'll be at +5 (+6 with Expertise) at level 1 vs F/R/W and that's pretty darn good.
For a STR cleric I'd say get light/heavy shield and start with at least a 13 CON (dwarf with an 11 + 2 is good here) so you can pick up Scale and by level 21 (with 11/21 stat bumps) you can finally get plate.
For the WIS cleric it's more stat dependent and without knowing how he allocated it's hard to say. IMO the "laser" Cleric has MAD issues as regards defenses. Either you accept that he's gonna get hit more often, or you sacrifice your to-hit in order to pick up STR/CON so you can get scale and a heavy shield. Either way you're going to have problems. I've also seen suggested an Elf Cleric starting with a 16/16 -> 18/18 WIS/DEX. This can give you a 17 AC (with Hide) at 1st level and a decent to-hit as well as being able to use a longbow ranged basic attack, or you can try to squeeze a 13 STR in there for a shield and have a 20 AC by level 2.
As for him not hitting well that also depends a lot on his stats. Expertise is good for anyone needing to hit. For the STR cleric I advise picking up any +3 weapon proficiency (long sword, bastard sword) because for a Cleric it's more about getting the buffs than the damage he does. For the WIS "laser" Cleric there's not much more to do than start with an 18/14/11 array and put the 18 in WIS and be sure to pick a race that bumps WIS to 20. You'll be at +5 (+6 with Expertise) at level 1 vs F/R/W and that's pretty darn good.