Last War: Survival rewards a focused start far more than it rewards spending. The first few days set the pace for everything after, so a little discipline early goes a long way.
Finish the guided tutorial questline first - it hands out enough free resources and heroes to jumpstart your base meaningfully, and skipping ahead just means missing free value. Keep both your building queue and research queue running at all times; an idle queue is wasted time you can never get back, so always have something in progress even if it's not optimal.
Join an active alliance as early as possible. Alliance Tech (funded by member donations) unlocks passive, account-wide bonuses that compound over time, and a good alliance also means help with rallies, protection from bullies, and someone to answer questions. Don't be picky about your first alliance - you can always transfer later once you understand the server better.
Avoid two common early mistakes: spending gems on cosmetics or random pulls instead of direct power purchases, and attacking players or rallies well above your own power out of impatience. Growth compounds - a strong foundation in week one pays off for months.