A while ago, I wrote a fitting guide for my alt's corpmates. They were miners and missioners but they were willing to fight (we do periodic low-sec roam). It wasn't realistic to give a disparate group specific fits, so I wrote a general guide. I then realized this would be useful for RvB members and well, anyone new to PvP.
1: prop mods. It's debatable if afterburner or microwarpdrive are the best (I prefer the latter), but for the love of god, have one! Speed is life in PvP, especially for frigates. If you do want to use a low slot for a speed module, nanofibres are better than over drive because they also make you more agile.
2: Tanking. If there is logi support (ie a ship that can heal others, ie a "cleric"), it will help if you have the same tank type as the logi is repairing (this mean shield or armour). Active tank can work, but only in very small gangs - even a medium fleet will completely overwhelm your reper, and buffer is better. For the love of god, do not dual tank (shield or armor, never both)! There are some rare instances where it makes sense, but 99.9% of the time, it doesn't. If you can fit/afford a t2 tank, do so. Lastly, the most important tank mod you can have is damage control, having one on your ship will help you survive longer.
3: Damage: We will not be shooting rats for hours - rather other people for minutes, and they will be trying to blow us up too! It's a race. So don't cheap out on ammo - get t2 ammo or faction ammo. You won't need more than a load or two, you will get blown up sooner or later anyway. If you are concerned about running out, bring t1 backup ammo. Tech2 drones are also really good. Seriously consider training Thermodynamics so you can overheat your guns to get that 20% dps boost when it really matters. (it's really a good skill to have for PvP in general, not just gunnery). I recommend to have one rig or one low slot devoted to DPS boost - don't go nuts, but it really helps.
Of course, *please* use the appropriate weapons for your ship - whatever your ship gives a bonus for DPS, use that! Also, your weapons should match. Never ever fit a mixture of short and long range weapons.
If you have a free high slot, put some capacitor warfare - neut or nos, or simply leave empty.
4: Rigs: It's a good idea to use them, but use t1 version, the t2 are too expensive for t1 frigs. Rigs allow you to "fix" weaknesses in your ships - tank, dps etc, or to enhance a strong point.
5: Tech levels: If you can use tech 2 modules and can afford it, go ahead. If you want to save money... don't use tech 1. Use meta 1-2, its frequently cheaper and gives you better performance. Meta4 are easy to fit and give good performance, but sometimes are more expensive than tech 2. In some cases (esp ewar) meta4 are strictly better than t2.
6: Mid slots: It's absolutely essential you have some kind of tackle mod - a web and or a warp scram/disrupter The only exception is if you are a sniper (and I don't know many sniping frigates...). If you have room to spare, strongly give thought to some ewar ( turret disruption, sensor dampers or target painter). You will note that doesn't leave a lot of room for your tank if you are a shield tanker - again, rigs and damage control will help make up for that.
7: Speaking of capacitor: you don't need to be stable, only last a few minutes (again, this isn't PvE). However if you only have capacitor for 20 seconds, use cap boosters (NOT a cap recharger).
8: You may need a fitting low-slot mod to boost CPU or Power grid (or a rig). However if you need more than one, you are either trying to do "too much" with the ship, or need more fitting skills training. If you are very close, try using a better meta-version of a mod. For example, one corpmate was 0.5 CPU short of being able to fit a damage control on his frigate. By switching his web and his prop mod from tech 1 to meta fits, he was able to gain enough CPU to fit it and thus greatly improve his tank.
9. Look up EFT (see https://forums.eveonline.com/default.aspx?g=posts&t=24359). It's a bit tricky to use but will allow you to test fits without having to actually buy anything.
10: Stacking penalties. Apart from weapons (ha), adding several of the same modules will give you a penalty to the bonus provided. The first module is 100% effective. The second one will be 87% effective, the third one 57%... on a ship with several slots, it can make sense to have say, 3 ballistic control systems, but on a frigate, slots are few. It's rarely worth putting more than 2 of the same module.
I say "rules" incidentally because these are more guidelines than rules. They can be broken if you know what you are doing! But in general, these will serve you well.