Trouble starting

My 1989 Sentra will not start easily at first start of the day. When this first happened I changed the fuel filter and it seemed to help. However I am still having the same problem, intermitently. The engine kicks over but will not catch, I keep trying and eventually it starts with great difficulty. The weird part is after it starts that first time it starts with no problem for the rest of the day. Also while driving it will run rough and feels like it is missing again intermitently. I was told it cannot be the fuel pump because it would not run at all if it was out.
I'm thinking the plugs, or maybe the injecters are going.
Also, I have no idea how to get to the plugs, they have these plastic covers on the wires that I cannot get past.
Any advice you can give would be greatly appreciated!
Thanks, Drew