A few basic things first of all
*blue is better when attacking. If you attack with halberdiers or the 'green' soldiers you will lose more. If you feel you have to use these soldiers to attack then for god sake use the 'strong vanguard' tactic when setting up your attack so they go in last!
*pack an attack with EVERYTHING you have (except green soldiers unless you feel as though you really have to). This is because outposts can be reinforced by the player you're attacking or their alliance. Don't expect to come up against what you see in your spy report
*use espionage if possible to get a good idea what your target has, if you can win and, most importantly, if you can win!
*THIS IS THE MOST IMPORTANT TIP! Use tools for everything... This means you need tools to combat moats, walls, the gate and defensive tools including bulwarks and other tools which boost ranged units defensive stats. If you don't use these you can send literally thousands of the best soldiers and I personally guarantee you will lose lol. NO TOOLS NO WIN- not if you're planning on catching a big fish.
UNITS- The best units to attack with hour travelling knights, followed by veterans (unlocked by research), then heavy crossbow man and twohanded swords, followed by crossbowan and macemen then finally you have the defensive 'green' soldiers who are useless at attacking and I recommend you don't use when attacking. Obviously you should use the best units available to you! So if you have vets and travelling knights available use them and also make sure you unlock these units when they become available.
TOOLS-ruby tools are best, make sure you use tools for each of your targets defences and pack them high!
SETTING UP AN ATTACK- use your strongest units on the flanks as you can fit fewer numbers here and so in order to get an attack number equal or closer to what you have on the front- follow this advice! You will win fights on the flanks more often and of course if you win on the front gate and flanks you'll get +30% in the courtyard fight (0% bonus if you win on two flanks out of the three and -30% on just one) which also means it's very important to attack all three flanks!
I normally use a 50/50 mix of melee and ranged attackers as this way the defender cannot get an advantage on you through clever defensive set ups... But if your target is known to you as not being tactical and has all ranged defenders on one flank then probably best to send all melee soldiers on this flank.
A FEW THINGS TO CONSIDER-
*time attacks to land in early hours of morning so you target and their alliance are less likely to be online and defend
*attack the weakest outpost of your opponent if you want an easy win and HONOUR and if you want GLORY use banners and attack a food outpost
*the larger your attack force the earlier the defender will see it on the map and the better your stable and hoorses are the less time your opponent has between the attack showing up and your attack landing
*your target might retaliate or get support so probably best to avoid players in top alliances unless you attack en mass with the rest of your alliance or unless you're in a top alliance yourself
*tower and wall upgrades make your life harder! avoid them where possible
*CHECK YOUR TARGET FIRST BY SELECTING THEIR CASTLE AND THENS ELECTING ATTACK- this will show you how much honour you will get from attacking them and whether you will get glory points. ALSO REMEMBER THAT IF YOU ARE NOT GETTING MUCH HONOUR FROM THE TARGET AND THEN YOUR TARGET LOSES HONOUR YOU MAY WELL NOT GET HONOUR FROM YOU ATTACK ANYMORE AND YOU MAY EVEN LOSE HONOUR