[Alneyan]

I almost always go with Construction, Mines and Fighters early on myself (it should be over around turn 20 or before). Mines are a powerful defence early on, Fighters are a mobile defence, and Light Carriers are adequate vessels (about the same as Light Cruisers, with in-built cargo and more hitpoints, but easier to hit and somewhat more expensive). Light Carriers also make very good minelayers, as they are able to lay many mines on a single turn while carrying quite a few such mines.

I believe your problem with warships and technology was that you did not expand enough: expansion is a key part of the game, as the more colonies you have, the merrier (and the more powerful you will be). Colony ships are cheap to build, and they can be sent to several systems away to build a forward spaceyard there, which in turn will produce more spaceyards to claim more systems.

Your best bet for defence in the expansion phase are those Mines: they pack quite a punch, and several Minesweepers will be needed to remove them. By the time someone else has the means to build a small fleet and enough minesweepers, you should hopefully have a solid economy, allowing you to build adequate vessels. The AI may be eager to get into early wars however, much more so than human players, so this may be a problem (though you spoke of Dreadnoughts, so I guess it was later in the game).