I want to share my thoughts on possible strategies in FE: LH. I will also try to provide some useful insight into game mechanics as well as some tips and tricks.
FE:LH is a fantasy themed 4x game with RPG elements. The aim of the game is to bring order to the torn world of Elemental. It can be done by vanquishing all other players, allying all other fractions, completing the master quest, or by casting the spell of making. My intent is to write a guide for Normal and Challenging diffictulty with more Kingdom/Empire setting and for beginners and intermediate players, so some of the tips may not be accurate for higher difficulty settings or with all players of adverse alignment.
1) When you choose the starting starting location I advise you to build a pioneer. The early stage of the game is very hectic because every computer player tries to build as much cities as possible. Please bear it in mind that cities are the primary factor that determines the performance of your Empire/Kingdom. Your performance in the early game determines how much revenue you are going to get from taxation, how fast you will discover new technologies, how fast you will be able to train units and how good they will be. I always make my capital a town, so I can sustain positive income in early and possibly in mid and late stage of the game. The second settlement is a Conclave/Fortress depending on the circumstances. I always build Conclave in my internal territory and Fortress near the border. I think that having 2 cities is minimum, 4 is optimal and 6 is max (mind the unrest penalty for every new city). I recommend using this preset for large/huge maps. On lesser maps rules are different.
2) As mentioned before the AI has expansionist mindset. Not only they will build cities, but they also will build a lot of outposts. So, if you don't want to be cut off at a certain point watch every pioneer unit that traverses your territory. Moreover, if you decide to build another city far away from your starting point and you skip a single patch of soil with 1 grain and 5 material be sure that AI will build a city there if of only they get a chance. Such a behavior is a pain in the neck, especially when you have to move army from point A to point B and you are asked to leave the territory. You are forced to declare war, which will have impact on your relations with players of the same alignment as the player who put the ultimatum.
3) After the borders are established there is an ephemeral period of peace. As the first step I recommend completely researching the tree of education (with some break for restoration and civics). If you are in close proximity with your neighbours start researching military techs with a break for civic techs when your cities maximal potential for your current technological state (e.g. population cap due to lack of food). Remember to research some magic tree. As a minimum discover shard harvesting, but do not go beyond arcane mastery (you need to establish a stable pool of mana etc.) Additional mana will help you cast essential enhancements such as tutolage, or meditation. Furthermore, researching military will not only give you better weapons, but it will allow you to have larger armies. Remeber that going for this build requires a stable income of iron.